Ramanaiah Mamillapalli

Genetic deletion of the Pten tumor suppressor gene promotes cell motility by activation of Rac1 and Cdc42 GTPases

Pten (Phosphatase and tensin homolog deleted on chromosome 10) is a recently identified tumor suppressor gene which is deleted or mutated in a variety of primary human cancers and in three cancer predisposition syndromes [1]. Pten regulates apoptosis and cell cycle progression through its phosphatase activity on phosphatidylinositol (PI) 3,4,5-trisphosphate (PI(3,4,5)P(3)), a product of PI 3-kinase [2-5]. Pten has also been implicated in controlling cell migration [6], but the exact mechanism is not very clear. Using the isogenic Pten(+/+) and Pten(-/-) mouse fibroblast lines, here we show that Pten deficiency led to increased cell motility. Reintroducing the wild-type Pten, but not the catalytically inactive Pten C124S or lipid-phosphatase-deficient Pten G129E mutant, reduced the enhanced cell motility of Pten-deficient cells. Moreover, phosphorylation of the focal adhesion kinase p125(FAK) was not changed in Pten(-/-) cells. Instead, significant increases in the endogenous activities of Rac1 and Cdc42, two small GTPases involved in regulating the actin cytoskeleton [7], were observed in Pten(-/-) cells. Overexpression of dominant-negative mutant forms of Rac1 and Cdc42 reversed the cell migration phenotype of Pten(-/-) cells. Thus, our studies suggest that Pten negatively controls cell motility through its lipid phosphatase activity by down-regulating Rac1 and Cdc42.

PTEN regulates the ubiquitin-dependent degradation of the CDK inhibitor p27KIP1 through the ubiquitin E3 ligase SCFSKP2

The PTEN tumor suppressor acts as a phosphatase for phosphatidylinositol-3,4,5-trisphosphate (PIP3) [1, 2]. We have shown previously that PTEN negatively controls the G1/S cell cycle transition and regulates the levels of p27(KIP1), a CDK inhibitor [3, 4]. Recently, we and others have identified an ubiquitin E3 ligase, the SCF(SKP2) complex, that mediates p27 ubiquitin-dependent proteolysis [5-7]. Here we report that PTEN and the PI 3-kinase pathway regulate p27 protein stability. PTEN-deficiency in mouse embryonic stem (ES) cells causes a decrease of p27 levels with concomitant increase of SKP2, a key component of the SCF(SKP2) complex. Conversely, in human glioblastoma cells, ectopic PTEN expression leads to p27 accumulation, which is accompanied by a reduction of SKP2. We found that ectopic expression of SKP2 alone is sufficient to reverse PTEN-induced p27 accumulation, restore the kinase activity of cyclin E/CDK2, and partially overcome the PTEN-induced G1 cell cycle arrest. Consistently, recombinant SCF(SKP2) complex or SKP2 protein alone can rescue the defect in p27 ubiquitination in extracts prepared from cells treated with a PI 3-kinase inhibitor. Our findings suggest that SKP2 functions as a critical component in the PTEN/PI 3-kinase pathway for the regulation of p27(KIP1) and cell proliferation.

Switching of G-protein Usage by the Calcium-sensing Receptor Reverses Its Effect on Parathyroid Hormone-related Protein Secretion in Normal Versus Malignant Breast Cells

The calcium-sensing receptor (CaR) is a G-protein-coupled receptor that signals in response to extracellular calcium and regulates parathyroid hormone secretion. The CaR is also expressed on normal mammary epithelial cells (MMECs), where it has been shown to inhibit secretion of parathyroid hormone-related protein (PTHrP) and participate in the regulation of calcium and bone metabolism during lactation. In contrast to normal breast cells, the CaR has been reported to stimulate PTHrP production by breast cancer cells. In this study, we confirmed that the CaR inhibits PTHrP production by MMECs but stimulates PTHrP production by Comma-D cells (immortalized murine mammary cells) and MCF-7 human breast cancer cells. We found that changes in intracellular cAMP, but not phospholipase C or MAPK signaling, correlated with the opposing effects of the CaR on PTHrP production. Pharmacologic stimulation of cAMP accumulation increased PTHrP production by normal and transformed breast cells. Inhibition of protein kinase A activity mimicked the effects of CaR activation on inhibiting PTHrP secretion by MMECs and blocked the effects of the CaR on stimulating PTHrP production in Comma-D and MCF-7 cells. We found that the CaR coupled to Gαi in MMECs but coupled to Gαs in Comma-D and MCF-7 cells. Thus, the opposing effects of the CaR on PTHrP production are because of alternate G-protein coupling of the receptor in normal versus transformed breast cells. Because PTHrP contributes to hypercalcemia and bone metastases, switching of G-protein usage by the CaR may contribute to the pathogenesis of breast cancer.

The calcium-sensing receptor couples to Gαs and regulates PTHrP and ACTH secretion in pituitary cells

The calcium-sensing receptor (CaR or CASR as listed in the MGI Database) is a G protein-coupled receptor that binds and signals in response to extracellular calcium and other polycations. It is highly expressed on parathyroid and kidney cells, where it participates in the regulation of systemic calcium homeostasis. It is also expressed on many other cell types and is involved in a wide array of biological functions such as cell growth and differentiation, ion transport, and hormone secretion. It has been described to couple to several different G proteins including Galpha(i/0), Galpha(q/11), and Galpha(12/13). Recently, it has also been shown to stimulate cAMP production by coupling to Galpha(s) in immortalized or malignant breast cells. The CaR is expressed on cells in the anterior pituitary and had previously been described to stimulate cAMP production in these cells. In this report, we examined signaling from the CaR in murine pituitary corticotroph-derived, AtT-20 cells. We found that CaR activation led to the stimulation of cAMP production, and PTH-related protein (PTHrP or PTHLH as listed in the MGI Database) and ACTH secretion from these cells. Furthermore, manipulation of cAMP levels was able to modulate PTHrP and ACTH secretion independent of changes in extracellular calcium. Finally, we demonstrated that the CaR couples to Galpha(s) in AtT-20 cells. Therefore, in pituitary corticotroph-like cells, as in breast cancer cells, the CaR utilizes Galpha(s) and activates cAMP production to stimulate hormone secretion.

Mammary-Specific Ablation of the Calcium-Sensing Receptor During Lactation Alters Maternal Calcium Metabolism, Milk Calcium Transport, and Neonatal Calcium Accrual

To meet the demands for milk calcium, the lactating mother adjusts systemic calcium and bone metabolism by increasing dietary calcium intake, increasing bone resorption, and reducing renal calcium excretion. As part of this adaptation, the lactating mammary gland secretes PTHrP into the maternal circulation to increase bone turnover and mobilize skeletal calcium stores. Previous data have suggested that, during lactation, the breast relies on the calcium-sensing receptor (CaSR) to coordinate PTHrP secretion and milk calcium transport with calcium availability. To test this idea genetically, we bred BLG-Cre mice with CaSR-floxed mice to ablate the CaSR specifically from mammary epithelial cells only at the onset of lactation (CaSR-cKO mice). Loss of the CaSR in the lactating mammary gland did not disrupt alveolar differentiation or milk production. However, it did increase the secretion of PTHrP into milk and decreased the transport of calcium from the circulation into milk. CaSR-cKO mice did not show accelerated bone resorption, but they did have a decrease in bone formation. Loss of the mammary gland CaSR resulted in hypercalcemia, decreased PTH secretion, and increased renal calcium excretion in lactating mothers. Finally, loss of the mammary gland CaSR resulted in decreased calcium accrual by suckling neonates, likely due to the combination of increased milk PTHrP and decreased milk calcium. These results demonstrate that the mammary gland CaSR coordinates maternal bone and calcium metabolism, calcium transport into milk, and neonatal calcium accrual during lactation.

Chemoattraction of bone marrow-derived stem cells towards human endometrial stromal cells is mediated by estradiol regulated CXCL12 and CXCR4 expression.

Bone marrow derived cells engraft to the uterine endometrium and contribute to endometriosis. The mechanism by which these cells are mobilized and directed to the endometrium has not been previously characterized. We demonstrate that human endometrial stromal cells (hESCs) produce the chemokine CXCL12 and that bone marrow cells (BMCs) express the CXCL12 receptor, CXCR4. Treatment with physiological levels of estradiol (E2) induced both CXCL12 and CXCR4 expression in hESCs and BMCs, respectively. BMCs migrated towards hESCs conditioned media; a CXCR4 antagonist blocked migration indicating that CXCL12 acting through its receptor, CXCR4, is necessary for chemoattraction of BM cells to human endometrial cells. E2 increased both CXCL12 expression in endometrial cells and CXCR4 expression in BM cells, further enhancing chemoattraction. E2 induced CXCL12/CXCR4 expression in endometrium and BM, respectively, drives migration of stem cells to the endometrium. The E2-CXCL12/CXCR4 signaling pathway may be useful in determining treatments for endometrial disorders, and may be antagonized to block stem cell migration to endometriosis.

Serum microRNAs as diagnostic markers of endometriosis: a comprehensive array-based analysis

OBJECTIVE To investigate serum microRNAs (miRNAs) in women with endometriosis. DESIGN Case-control study. SETTING University hospital. PATIENT(S) Women with (n = 24) and without (n = 24) endometriosis. INTERVENTION(S) Serum samples were obtained from surgically diagnosed subjects. MAIN OUTCOME MEASURE(S) miRNA from women with without endometriosis were used for microarray profiling and confirmed by means of quantitative real-time polymerase chain reaction (qRT-PCR). Receiver operating characteristic (ROC) analysis was performed on differentially expressed miRNAs. RESULT(S) miR-3613-5p, miR-6755-3p were down-regulated and miR-125b-5p, miR-150-5p, miR-342-3p, miR-143-3p, miR-145-5p, miR-500a-3p, miR-451a, miR-18a-5p were up-regulated more than 10-fold in the microarray. These results were confirmed with the use of qRT-PCR. Among the differentially expressed miRNAs, miR-125b-5p expression levels had the highest area under the ROC curve (AUC). The maximum AUC score of 1.000 was achieved when combining miR-125b-5p, miR-451a, and miR-3613-5p with the use of a logistic regression model. CONCLUSION(S) We identified several miRNAs in serum that distinguished subjects with endometriosis from those without. miR-125b-5p had the greatest potential as a single diagnostic biomarker. A combination of that miRNA with miR-451a and miR-3613-5p further improved diagnostic performance.

Endometriosis Located Proximal to or Remote From the Uterus Differentially Affects Uterine Gene Expression

The mechanisms that lead to the altered uterine gene expression in women with endometriosis are poorly understood. Are these changes in gene expression mediated by proximity to endometriotic lesions or is endometriosis a systemic disease where the effect is independent of proximity to the uterus? To answer this question, we created endometriosis in a murine model either in the peritoneal cavity (proximal) or at a subcutaneous remote site (distal). The expression of several genes that are involved in endometrial receptivity (homeobox A10 [Hoxa10], homeobox A11 [Hoxa11], insulin-like growth factor binding protein 1 [Igfbp1], Kruppel-like factor 9 [Klf9], and progesterone receptor [Pgr]) was measured in the eutopic endometrium of mice transplanted with either proximal or distal endometriosis lesions. Decreased expression of Hoxa10, Igfbp1, Klf9, and total Pgr genes was observed in the eutopic endometrium of mice with peritoneal endometriosis. In the mice with distal lesions, overall expression of these genes was not as severely affected, however, Igfbp1 expression was similarly decreased and the effect on Pgr was more pronounced. Endometriosis does have a systemic effect that varies with distance to the end organ. However, even remote disease selectively and profoundly alters the expression of genes such as Pgr. This is the first controlled experiment demonstrating that endometriosis is not simply a local peritoneal disease. Selective alteration of genes critical for endometrial receptivity and endometriosis propagation may be systemic. Similarly, systemic effects of endometriosis on other organs may also be responsible for the widespread manifestations of the disease.

The broad-spectrum receptor tyrosine kinase inhibitor dovitinib suppresses growth of BRAF-mutant melanoma cells in combination with other signaling pathway inhibitors

BRAF inhibitors have revolutionized treatment of mutant BRAF metastatic melanomas. However, resistance develops rapidly following BRAF inhibitor treatment. We have found that BRAF‐mutant melanoma cell lines are more sensitive than wild‐type BRAF cells to the small molecule tyrosine kinase inhibitor dovitinib. Sensitivity is associated with inhibition of a series of known dovitinib targets. Dovitinib in combination with several agents inhibits growth more effectively than either agent alone. These combinations inhibit BRAF‐mutant melanoma and colorectal carcinoma cell lines, including cell lines with intrinsic or selected BRAF inhibitor resistance. Hence, combinations of dovitinib with second agents are potentially effective therapies for BRAF‐mutant melanomas, regardless of their sensitivity to BRAF inhibitors.

Bone Marrow Stem Cell Chemotactic Activity Is Induced by Elevated CXCl12 in Endometriosis

Endometriosis is an inflammatory gynecological disorder caused by the growth of endometrial tissue outside the uterus. Endometriosis produces chemokines, including CXCL12, that attract bone marrow cells to the lesions. In this study, we describe the expression, localization, and chemotactic activity of CXCL12 in endometriotic lesions. Biopsies were collected both from women with endometriosis undergoing laparoscopy and control endometrium from women without endometriosis. Expression of CXCl12 and CXCR4 messenger RNA was increased approximately 4- and 6-fold, respectively, in endometriosis compared to eutopic endometrium. Immunohistochemistry of lesions revealed that CXCR4 was expressed in the stroma and epithelium in both endometriosis and control eutopic endometrium. The level of CXCR4 protein expression was significantly higher in all cellular compartments of the endometriotic lesions compared to control endometrium. CXCL12 protein expression was also higher in endometriotic lesions and was greatest in the epithelial compartment. CXCL12 was increased more in the condition media of cultured endometriosis than in controls as measured by enzyme-linked immunosorbent assay. Transwell chamber migration was used to demonstrate 2-fold increased chemoattraction of mouse bone marrow stem cells toward CXCL12 in the endometriotic-conditioned medium compared with eutopic endometrium. Our results indicate that a preferential recruitment of stem cells to endometriosis can explain how endometriosis outcompetes eutopic endometrium in recruiting the limited supply of circulating stem cells. The CXCL12/CXCR4 signaling axis is a potential target for the treatment of endometriosis and its associated disorders.Endometriosis is an inflammatory gynecological disorder caused by the growth of endometrial tissue outside the uterus. Endometriosis produces chemokines, including CXCL12, that attract bone marrow cells to the lesions. In this study, we describe the expression, localization, and chemotactic activity of CXCL12 in endometriotic lesions. Biopsies were collected both from women with endometriosis undergoing laparoscopy and control endometrium from women without endometriosis. Expression of CXCl12 and CXCR4 messenger RNA was increased approximately 4- and 6-fold, respectively, in endometriosis compared to eutopic endometrium. Immunohistochemistry of lesions revealed that CXCR4 was expressed in the stroma and epithelium in both endometriosis and control eutopic endometrium. The level of CXCR4 protein expression was significantly higher in all cellular compartments of the endometriotic lesions compared to control endometrium. CXCL12 protein expression was also higher in endometriotic lesions and was greatest in the epithelial compartment. CXCL12 was increased more in the condition media of cultured endometriosis than in controls as measured by enzyme-linked immunosorbent assay. Transwell chamber migration was used to demonstrate 2-fold increased chemoattraction of mouse bone marrow stem cells toward CXCL12 in the endometriotic-conditioned medium compared with eutopic endometrium. Our results indicate that a preferential recruitment of stem cells to endometriosis can explain how endometriosis outcompetes eutopic endometrium in recruiting the limited supply of circulating stem cells. The CXCL12/CXCR4 signaling axis is a potential target for the treatment of endometriosis and its associated disorders.