Alejandro López-Saavedra

Cytoplasmic p21CIP1/WAF1, ERK1/2 activation, and cytoskeletal remodeling are associated with the senescence-like phenotype after airborne particulate matter (PM10) exposure in lung cells

The exposure to particulate matter with a mean aerodynamic diameter ≤10 μm (PM10) from urban zones is considered to be a risk factor in the development of cancer. The aim of this work was to determine if PM10 exposure induces factors related to the acquisition of a neoplastic phenotype, such as cytoskeletal remodeling, changes in the subcellular localization of p21(CIP1/WAF1), an increase in β-galactosidase activity and changes in cell cycle. To test our hypothesis, PM10 from an industrial zone (IZ) and a commercial zone (CZ) were collected, and human adenocarcinoma lung cell cultures (A549) were exposed to a sublethal PM10 concentration (10 μg/cm(2)) for 24 h and 48 h. The results showed that PM10 exposure induced an increase in F-actin stress fibers and caused the cytoplasmic stabilization of p21(CIP1/WAF1) via phosphorylation at Thr(145) and Ser(146) and the phosphorylation of ERK1/2 on Thr(202). Changes in the cell cycle or apoptosis were not observed, but an increase in β-galactosidase activity was detected. The PM10 from CZ caused more dramatic effects in lung cells. We conclude that PM10 exposure induced cytoplasmic p21(CIP1/WAF1) retention, ERK1/2 activation, cytoskeleton remodeling and the acquisition of a senescence-like phenotype in lung cells. These alterations could have mechanistic implications regarding the carcinogenic potential of PM10.

Internalization of titanium dioxide nanoparticles by glial cells is given at short times and is mainly mediated by actin reorganization-dependent endocytosis

Many nanoparticles (NPs) have toxic effects on multiple cell lines. This toxicity is assumed to be related to their accumulation within cells. However, the process of internalization of NPs has not yet been fully characterized. In this study, the cellular uptake, accumulation, and localization of titanium dioxide nanoparticles (TiO2 NPs) in rat (C6) and human (U373) glial cells were analyzed using time-lapse microscopy (TLM) and transmission electron microscopy (TEM). Cytochalasin D (Cyt-D) was used to evaluate whether the internalization process depends of actin reorganization. To determine whether the NP uptake is mediated by phagocytosis or macropinocytosis, nitroblue tetrazolium (NBT) reduction was measured and the 5-(N-ethyl-N-isopropyl)-amiloride was used. Expression of proteins involved with endocytosis and exocytosis such as caveolin-1 (Cav-1) and cysteine string proteins (CSPs) was also determined using flow cytometry. TiO2 NPs were taken up by both cell types, were bound to cellular membranes and were internalized at very short times after exposure (C6, 30 min; U373, 2h). During the uptake process, the formation of pseudopodia and intracellular vesicles was observed, indicating that this process was mediated by endocytosis. No specific localization of TiO2 NPs into particular organelles was found: in contrast, they were primarily localized into large vesicles in the cytoplasm. Internalization of TiO2 NPs was strongly inhibited by Cyt-D in both cells and by amiloride in U373 cells; besides, the observed endocytosis was not associated with NBT reduction in either cell type, indicating that macropinocytosis is the main process of internalization in U373 cells. In addition, increases in the expression of Cav-1 protein and CSPs were observed. In conclusion, glial cells are able to internalize TiO2 NPs by a constitutive endocytic mechanism which may be associated with their strong cytotoxic effect in these cells; therefore, TiO2 NPs internalization and their accumulation in brain cells could be dangerous to human health.

Airborne particulate matter in vitro exposure induces cytoskeleton remodeling through activation of the ROCK-MYPT1-MLC pathway in A549 epithelial lung cells

Airborne particulate matter with an aerodynamic diameter ≤10μm (PM10) is considered a risk factor for the development of lung cancer. Little is known about the cellular mechanisms by which PM10 is associated with cancer, but there is evidence that its exposure can lead to an acquired invasive phenotype, apoptosis evasion, inflammasome activation, and cytoskeleton remodeling in lung epithelial cells. Cytoskeleton remodeling occurs through actin stress fiber formation, which is partially regulated through ROCK kinase activation, we aimed to investigate if this protein was activated in response to PM10 exposure in A549 lung epithelial cells. Results showed that 10μg/cm2 of PM10 had no influence on cell viability but increased actin stress fibers, cytoplasmic ROCK expression, and phosphorylation of myosin phosphatase-targeting 1 (MYPT1) and myosin light chain (MLC) proteins, which are targeted by ROCK. The inhibition of ROCK prevented actin stress fiber formation and the phosphorylation of MYPT1 and MLC, suggesting that PM10 activated the ROCK-MYPT1-MLC pathway in lung epithelial cells. The activation of ROCK1 has been involved in the acquisition of malignant phenotypes, and its induction by PM10 exposure could contribute to the understanding of PM10 as a risk factor for cancer development through the mechanisms associated with invasive phenotype.

The role of alternative mRNA splicing in chromosome instability

Chromosomal instability (CIN) involves the gain or loss of complete or partial chromosomes during cellular division, and it is a common characteristic of tumors that have aneuploidy. In addition, CIN is considered to be a closely related event to carcinogenesis. The mechanisms that lead to CIN include defects in the cohesion of sister chromatids, mitotic spindle checkpoint, and regulation of the number of centrosomes. Different studies have found that transcription variants, also known as isoforms, which are generated by the alternative splicing of exons and introns in mRNA that encodes many of the regulator proteins of chromosomal segregation, have an important role in mechanisms that lead to CIN. The majority of these isoforms are newly described. The discovery of additional isoforms and the study of their mechanisms of action allow a more integrated view of how cells regulate the segregation of their genetic material, and of how errors occur in chromosomal segregation.

Secretome derived from breast tumor cell lines alters the morphology of human umbilical vein endothelial cells

Abstract Metastases, responsible for most of the solid tumor associated deaths, require angiogenesis and changes in endothelial cells. In this work, the effect of the secretomes of three breast tumor cell lines (MCF-7, MDA-MB-231 and ZR-75-30) on human umbilical vein endothelial cells (HUVEC) morphology was investigated. HUVEC treated with secretomes from breast cells were analyzed by confocal and time-lapse microscopy. Secretomes from ZR-75-30 and MDA-MB-231 cells modify the morphology and adhesion of HUVEC. These changes may provoke the loss of endothelial monolayer integrity. In consequence, tumor cells could have an increased access to circulation, which would then enhance metastasis.

Function of HP1 proteins as a component in kinetochore formation and its relation with chromosome instability

HP1 Family of proteins are involved in the formation and maintenance of chromatin higher order structure. In mammals there are known three isotypes (HP1a, HP1b and HP1g). Recently, it has been proposed that HP1 may play an important roll in inner centromere establishment, generated by its interaction with HMis12 complex, (HMis12C) which is relevant in kinetochore formation and microtubule recognition which ensure correct chromosomal segregation. However, alterations in chromatin structure or loss in H3K9 methylation lead to a reduction of the protein presence and changes of HP1 proteins localization to heterochromatin followed by chromosome instability. It has not been studied if this is mediated by loss of recruitment of HMis12C to the kinetochore and which is it relation with chromosomal instability generation. Thus, the aim of this study is to determine if alteration of HP1 proteins is capable of reducing HMis12C recruitment to the kinetochore. We elaborated transfected of constructions of HP1-GFP for each isotype in HCT116 cells and performed time-lapse to observe localization along cell cycle by confocal microscopy; in addition, we treated cells with TSA 1uM to analyze changes in HP1 localization. We used ChIP assay in satellite alpha and satellite 2 to determine presence of H3H9me3, HP1 proteins, CENPA, and HMis12 in normal HCT116 and in HCT116 transfected cells with HP1-GFP and with Jmjd2b to observe the effect of the loss of H3K9me3 to HMis12C incorporation. We found that each isotype present a different localization at interphase, but HP1a and b are present at the centromere at this fase, also this localization is highly dynamic in mitosis where HP1b is removed and HP1a is enriched at the chromosomes centromere. Treatment with TSA increases chromosome instability and generates relocalization of HP1 proteins to pericentromeric chromatin where H3K9me3 remains and propagates. Jmjd2b over-expression reduces HP1 presence at chromatin and also reduces HMis12 in mitosis. These results support another function of HP1 as a kinetochore partner leading incorporation of HMis12 during cell division. This work was supported by CONACYT 83959 and PAPIITIN213311

BUB1 and SURVIVIN proteins are not degraded after a prolonged mitosis and accumulate in the nuclei of HCT116 cells.

Spindle poisons activate the spindle assembly checkpoint and prevent mitotic exit until cells die or override the arrest. Several studies have focused on spindle poison-mediated cell death, but less is known about consequences in cells that survive a mitotic arrest. During mitosis, proteins such as CYCLIN B, SECURIN, BUB1 and SURVIVIN are degraded in order to allow mitotic exit, and these proteins are maintained at low levels in the next interphase. In contrast, exit from a prolonged mitosis depends only on degradation of CYCLIN B; it is not known whether the levels of other proteins decrease or remain high. Here, we analyzed the levels and localization of the BUB1 and SURVIVIN proteins in cells that escaped from a paclitaxel-mediated prolonged mitosis. We compared cells with a short arrest (HCT116 cells) with cells that spent more time in mitosis (HT29 cells) after paclitaxel treatment. BUB1 and SURVIVIN were not degraded and remained localized to the nuclei of HCT116 cells after a mitotic arrest. Moreover, BUB1 nuclear foci were observed; BUB1 did not colocalize with centromere proteins. In HT29 cells, the levels of BUB1 and SURVIVIN decreased during the arrest, and these proteins were not present in cells that reached the next interphase. Using time-lapse imaging, we observed morphological heterogeneity in HCT116 cells that escaped from the arrest; this heterogeneity was due to the cytokinesis-like mechanism by which the cells exited mitosis. Thus, our results show that high levels of BUB1 and SURVIVIN can be maintained after a mitotic arrest, which may promote resistance to cell death.

MAD2γ, a novel MAD2 isoform, reduces mitotic arrest and is associated with resistance in testicular germ cell tumors

ABSTRACT Background: Prolonged mitotic arrest in response to anti-cancer chemotherapeutics, such as DNA-damaging agents, induces apoptosis, mitotic catastrophe, and senescence. Disruptions in mitotic checkpoints contribute resistance to DNA-damaging agents in cancer. MAD2 has been associated with checkpoint failure and chemotherapy response. In this study, a novel splice variant of MAD2, designated MAD2γ, was identified, and its association with the DNA damage response was investigated. Methods: Endogenous expression of MAD2γ and full-length MAD2 (MAD2α) was measured using RT-PCR in cancer cell lines, normal foreskin fibroblasts, and tumor samples collected from patients with testicular germ cell tumors (TGCTs). A plasmid expressing MAD2γ was transfected into HCT116 cells, and its intracellular localization and checkpoint function were evaluated according to immunofluorescence and mitotic index. Results: MAD2γ was expressed in several cancer cell lines and non-cancerous fibroblasts. Ectopically expressed MAD2γ localized to the nucleus and reduced the mitotic index, suggesting checkpoint impairment. In patients with TGCTs, the overexpression of endogenous MAD2γ, but not MAD2α, was associated with resistance to cisplatin-based chemotherapy. Likewise, cisplatin induced the overexpression of endogenous MAD2γ, but not MAD2α, in HCT116 cells. Conclusions: Overexpression of MAD2γ may play a role in checkpoint disruption and is associated with resistance to cisplatin-based chemotherapy in TGCTs.

Abstract 2728: In silico identification of a MAD2-interacting motif in MAD2 spliced isoforms suggest a functional interaction with the spindle assemble checkpoint in cancer

Abnormal chromosome segregation plays a key role in cancer development. MAD2 is a component of the spindle assembly checkpoint (SAC), a cell cycle control mechanism that ensures an accurate segregation of chromosomes during mitosis. Changes in MAD2 expression have been associated with chemo-resistance both to spindle inhibitors and to DNA damaging agents. Also, a previous study has shown that the exogenous expression of MAD2β, a splicing variant of MAD2, was associated with resistance to Adriamycin and Vincristine in gastric cell lines. Additionally, we have previously identified that exogenous overexpression of MAD2γ upon paclitaxel-induced SAC activation in the colorectal cancer cell HCT116, reduces drug-induced mitotic arrest. These findings suggested a possible structural interaction of MAD2 isoforms with SAC components. To determine possible structural interactions between MAD2 isoforms and key SAC components (i.e. MAD1 and CDC20), we performed an in silico analysis of MAD2 isoforms, Interestingly, we found that alternative splicing of MAD2 generates a premature stop codon and a frameshift in exon 4 in MAD2γ and MAD2β. This change generates a new C-terminal region in MAD2γ and MAD2β isoforms that comprise 16 amino acids, which are not present in the major isoform (MAD2α). We aligned this region with the amino acid sequence of CDC20 from various species and identified a MAD2-interacting motif (MIM). This finding suggests that MAD2 isoforms may interact with the active conformation of MAD2 (C-MAD2). Since MAD2 isoforms and CDC20 may compete for the same region in MAD2, we propose a new model whereby MAD2 isoforms inhibits SAC by interfering with C-MAD2/CDC20 formation. This model helps to explain previous results where MAD2 isoforms over expression seem to have an opposite role in SAC signaling. Citation Format: Miguel Ramirez-Otero, Alejandro Lopez-Saavedra, Marco Andonegui, Jose Diaz-Chavez, Luis Alonso Herrera. In silico identification of a MAD2-interacting motif in MAD2 spliced isoforms suggest a functional interaction with the spindle assemble checkpoint in cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2728.

Abstract 5457: MAD2γ, a new MAD2 isoform, is ubiquitously expressed in distinct cell lines, reduces mitotic arrest, and associates with resistance to cisplatin-based chemotherapy in testicular germ cell tumors

The mitotic spindle assembly checkpoint (SAC) signaling has been emerging as an important promising mechanism in cancer therapy. A prolonged mitotic arrest in response to cancer chemotherapy induces apoptosis, mitotic catastrophe, mitotic slippage and senescence, depending on what cell line and/or inhibitor is studied. In consequence, a weakened or disturbed SAC signaling in human cancers might contribute to drug resistance both to spindle inhibitors and to DNA damaging agents. In several studies the mitotic arrest deficient 2 (MAD2α) has been implicated in the association between failure in the SAC signaling and chemotherapy response. In this study, we identified a novel splicing variant of MAD2, designated as MAD2γ. This isoform was ubiquitously expressed in several cancer cell lines and non-cancerous primary foreskin fibroblasts. When it was ectopically expressed, MAD2γ localized in the nucleus. Its overexpression in a fully functional SAC-competent cancer cell line, HCT116, reduced the mitotic index, suggesting SAC impairment. Furthermore, the endogenous overexpression of MAD2γ in testicular germ cell tumor patients was associated with a resistant response to cisplatin-based chemotherapy, whereas expression of MAD2α was not significantly different between resistant and sensitive patients. In addition, HCT116 raised significantly its endogenous expression of MAD2γ only in response to cisplatin, but not that of MAD2α. Our data suggest that MAD2γ may have an opposing role to MAD2α in the activation of the SAC signaling, and that its expression is associated to a resistant response to DNA-damaging agents, such as cisplatin-based chemotherapy. This highlight the importance to study alternative splicing that may compromise the SAC function, which has been regarded as a promise for cancer therapy. Citation Format: Alejandro Lopez-Saavedra, Rodrigo Caceres, Fernando Luna, Irwin Hernandez, Luis Alonso Herrera. MAD2γ, a new MAD2 isoform, is ubiquitously expressed in distinct cell lines, reduces mitotic arrest, and associates with resistance to cisplatin-based chemotherapy in testicular germ cell tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5457. doi:10.1158/1538-7445.AM2015-5457