Toshiro Migita

ATP Citrate Lyase: Activation and Therapeutic Implications in Non–Small Cell Lung Cancer

Enhanced glucose and lipid metabolism is one of the most common properties of malignant cells. ATP citrate lyase (ACLY) is a key enzyme of de novo fatty acid synthesis responsible for generating cytosolic acetyl-CoA and oxaloacetate. To evaluate its role in lung cancer progression, we here analyzed ACLY expression in a subset of human lung adenocarcinoma cell lines and showed a relationship with the phosphatidyl-inositol-3 kinase-Akt pathway. The introduction of constitutively active Akt into cells enhanced the phosphorylation of ACLY, whereas dominant-negative Akt caused attenuation. In human lung adenocarcinoma samples, ACLY activity was found to be significantly higher than in normal lung tissue. Immunohistochemical analysis further showed phosphorylated ACLY overexpression in 162 tumors, well-correlating with stage, differentiation grade, and a poorer prognosis. Finally, to show the therapeutic potential and mechanism of ACLY inhibition for lung cancer treatment, we assessed the effect of RNA interference targeting ACLY on lipogenesis and cell proliferation in A549 cells. ACLY inhibition resulted in growth arrest in vitro and in vivo. Interestingly, increased intracellular lipids were found in ACLY knockdown cells, whereas de novo lipogenesis was inhibited. Supplementation of insulin could rescue the proliferative arrest elicited by ACLY inhibition; however, in contrast, fatty acid palmitate induced cell death. Taken together, these findings suggest that ACLY is involved in lung cancer pathogenesis associated with metabolic abnormality and might offer a novel therapeutic target.

Adult Xp11 Translocation Renal Cell Carcinoma Diagnosed by Cytogenetics and Immunohistochemistry

Purpose: To determine the incidence of Xp11 translocation renal cell carcinoma (RCC) in adult patients using cytogenetics and immunohistochemstry. Experimental Design: Cytogenetic studies were prospectively done using tumor samples from 443 consecutive adult Japanese patients (ages 15-89 years) who underwent nephrectomy for RCC. TFE3 immunohistochemistry was done for cases in which cytogenetic results were not obtained. Clinicopathologic characteristics of Xp11 translocation RCC were examined. Results: Mitotic cells suitable for cytogenetic analysis were obtained in 244 tumor samples (55%); among these, we identified 4 cases (1.6%) of Xp11 translocation RCC. TFE3 immunohistochemistry identified 3 positive cases (1.5%) among the remaining 199 cases. The median age of the 7 patients was 41 years (range, 15-59 years), and 15% of RCC patients (4 of 26) who were younger than ages 45 years had this type of RCC. Of the four Xp11 translocation RCC patients whose karyotypes were determined, two had an ASPL-TFE3 gene fusion. Of these 2, 1 had pulmonary metastasis at presentation, and the other developed liver metastasis 12 months after nephrectomy and died of the disease. The remaining two patients had PRCC-TFE3 and PSF-TFE3 gene fusions, respectively. Both had nodal involvement but remained disease free for 3 and 5 years, respectively, after surgical resection of lymph node metastases. Of the 3 immunohistochemically diagnosed patients, 1 had nodal metastases at presentation and died 9 months after surgery. Conclusions: This is the first report to determine the incidence of Xp11 translocation RCC in adult patients. We found that this disease is relatively common in young adults.

Increased expression of multidrug resistance-associated proteins in bladder cancer during clinical course and drug resistance to doxorubicin

Overexpression of the P‐glycoprotein/multidrug resistance 1 (MDR1) and multidrug resistance protein 1 (MRP1) gene is closely associated with the clinical outcome of various malignancies, and it is involved in responses to some anticancer chemotherapeutic agents including doxorubicin. Six human MRP subfamily members (MRP2‐7) with structural similarities to MRP1 have been identified. Recently, the relationships between MRP2 and MRP3 expression levels of some cancer cells and drug sensitivity to doxorubicin have been reported, but the relationship between the clinical samples and drug sensitivity remains unclear. We determined the expressions of the MDR1, MRP1, MRP2 and MRP3 gene in bladder cancer during the clinical course and sought to learn whether the expression was correlated with drug responses to doxorubicin. Doxorubicin, used in chemotherapeutic treatment including intravesical and systemic chemotherapy, is an important anticancer agent for the treatment of bladder cancer. We used quantitative reverse transcriptase‐polymerase chain reaction (RT‐PCR) analysis for our study, and the sensitivity to doxorubicin in bladder cancer was determined using the in vitro succinate dehydrogenase inhibition test. Using 47 clinical samples of bladder cancer, we confirmed the significant correlation of MDR1, MRP1 and MRP3 mRNA levels with resistance to doxorubicin. We showed that the expression of MDR1, MRP1, MRP2 and MRP3 in recurrent tumors and residual tumors after chemotherapeutic treatment was higher than that in untreated primary tumors. In particular, the MDR1 expression in residual tumors was 5.7‐fold higher than that in untreated primary tumors.

Downregulation of Cap43 gene by von Hippel‐Lindau tumor suppressor protein in human renal cancer cells

We previously identified 9 genes (i.e., thymosin β4, secreted protein acidic and rich in cysteine, Cap43, ceruloplasmin, serum amyloid A, heat shock protein 90, LOT1, osteopontin and casein kinase Iγ) that are more highly expressed in cancerous regions than in noncancerous regions in human renal cancers. In our study, we considered the possibility that the von Hippel‐Lindau (VHL) tumor suppressor gene might be able to affect the expression of these 9 genes in renal cancer cells. We first established 2 VHL‐positive cell lines, 786/VHL‐1 and 786/VHL‐2, after the introduction of wild‐type VHL into VHL‐negative renal cancer 786‐O cells. Of these 9 genes, expression of the Cap43 gene was specifically downregulated by VHL. Expression of Cap43 was also much lower in 4 other VHL‐positive renal cancer cell lines than in VHL‐negative 786‐O cells. Cap43 promoter assays with several deletion or mutation constructs demonstrated that the Sp1 site in the element from –286 base pairs (bp) to –62 bp was partly responsible for VHL‐induced suppression of the Cap43 gene. Immunostaining analysis with human specimens of renal cancers demonstrated that the Cap43 protein was expressed in most cancer cells and macrophages. We also observed a marked and specific increase of Cap43 mRNA levels in response to hypoxia or nickel in all VHL‐positive cell lines. Cellular expression of Cap43 mRNA in response to hypoxia or nickel thus is closely associated with VHL gene expression in renal cancer cells. Although the function of the Cap43 protein remains unclear, the expression of Cap43 protein could be a molecular marker closely associated with VHL in renal cancer.

Krüppel-like factor 12 plays a significant role in poorly differentiated gastric cancer progression

Gastric cancer is the second common malignant neoplasia in Japan, and its poorly differentiated form is a deadly disease. To identify novel candidate oncogenes contributing to its genesis, we examined copy‐number alterations in 50 primary poorly differentiated gastric cancers using an array‐based comparative genomic hybridization (array‐CGH). Many genetic changes were identified, including a novel amplification of the 13q22 locus. Several genes are located in this locus, and selective knockdown of one for the Krüppel‐like factor 12 (KLF12) induced significant growth‐arrest in the HGC27 gastric cancer cell line. Microarray analysis also demonstrated that genes associated with cell proliferation were mostly changed by KLF12 knockdown. To explore the oncogenic function of KLF12, we introduced a full length of human KLF12 cDNA into NIH3T3 and AZ‐521 cell lines and found that overexpression significantly enhanced their invasive potential. In clinical samples, KLF12 mRNA in cancer tissue was increased in 11 of 28 cases (39%) when compared with normal gastric epithelium. Clinicopathological analysis further demonstrated a significant correlation between KLF12mRNA levels and tumor size (p = 0.038). These data suggest that the KLF12 gene plays an important role in poorly differentiated gastric cancer progression and is a potential target of therapeutic measures.

Role of Insulin-Like Growth Factor Binding Protein 2 in Lung Adenocarcinoma: IGF-Independent Antiapoptotic Effect Via Caspase-3

Insulin-like growth factor (IGF) signaling plays a pivotal role in cell proliferation and mitogenesis. Secreted IGF-binding proteins (IGFBPs) are important modulators of IGF bioavailability; however, their intracellular functions remain elusive. We sought to assess the antiapoptotic properties of intracellular IGFBP-2 in lung adenocarcinomas. IGFBP-2 overexpression resulted in a decrease in procaspase-3 expression; however, it did not influence the phosphorylation status of either IGF receptor or its downstream targets, including Akt and extracellular signal-regulated kinase. Apoptosis induced by camptothecin was significantly inhibited by IGFBP-2 overexpression in NCI-H522 cells. Conversely, selective knockdown of IGFBP-2 using small-interfering RNA resulted in an increase in procaspase-3 expression and sensitization to camptothecin-induced apoptosis in NCI-H522 cells. LY294002, an inhibitor of phosphatidyl-inositol 3-kinase, caused a decrease in IGFBP-2 levels and enhanced apoptosis in combination with camptothecin. Immunohistochemistry demonstrated that intracellular IGFBP-2 was highly expressed in lung adenocarcinomas compared with normal epithelium. Intracellular IGFBP-2 and procaspase-3 were expressed in a mutually exclusive manner. These findings suggest that intracellular IGFBP-2 regulates caspase-3 expression and contributes to the inhibitory effect on apoptosis independent of IGF. IGFBP-2, therefore, may offer a novel therapeutic target and serve as an antiapoptotic biomarker for lung adenocarcinoma.

Telomere Length Influences Cancer Cell Differentiation In Vivo

ABSTRACT Limitless reproductive potential is one of the hallmarks of cancer cells. This ability is due to the maintenance of telomeres, erosion of which causes cellular senescence or death. While most cancer cells activate telomerase, a telomere-elongating enzyme, it remains elusive as to why cancer cells often maintain shorter telomeres than the cells in the surrounding normal tissues. Here, we show that forced telomere elongation in cancer cells promotes their differentiation in vivo. We elongated the telomeres of human prostate cancer cells that possess short telomeres by enhancing their telomerase activity. The resulting cells had long telomeres and retained the ability to form tumors in nude mice. Strikingly, these tumors exhibited many duct-like structures and reduced N-cadherin expression, reminiscent of well-differentiated adenocarcinoma. These changes were caused by telomere elongation and not by enhanced telomerase activity. Gene expression profiling revealed that tumor formation was accompanied by the expression of innate immune system-related genes, which have been implicated in maintaining tumor cells in an undifferentiated state and poor-prognosis cancers. In tumors derived from the telomere-elongated cells, upregulation of such gene sets is not observed. Our observations suggest a functional contribution of short telomeres to tumor malignancy by regulation of cancer cell differentiation.

Inhibition of ATP citrate lyase induces triglyceride accumulation with altered fatty acid composition in cancer cells.

De novo lipogenesis is activated in most cancers and several lipogenic enzymes have been implicated as therapeutic targets. Here, we demonstrate a novel function of the lipogenic enzyme, ATP citrate lyase (ACLY), in lipid metabolism in cancer cells. ACLY depletion by small interfering RNAs caused growth suppression and/or apoptosis in a subset of cancer cell lines. To investigate the effect of ACLY inhibition on lipid metabolism, metabolome and transcriptome analysis was performed. ACLY depletion blocks the fatty acid chain elongation from C16 to C18 in triglyceride (TG), but not in other lipid classes. Meanwhile, wild‐type ACLY overexpression enhanced fatty acid elongation of TG, whereas an inactive mutant ACLY did not change it. ACLY depletion‐mediated blockade of fatty acid elongation was coincident with downregulation of long‐chain fatty acid elongase ELOVL6, which resides in endoplasmic reticulum (ER). Paradoxically, ACLY depletion‐mediated growth suppression was associated with TG accumulation. ACLY depletion downregulated the expression of carnitine palmitoyltransferase 1A, which is a mitochondrial fatty acid transporter. Consistent with this finding, metabolome analysis revealed that ACLY positively regulates the carnitine system, which plays as an essential cofactor for fatty acid transport across mitochondrial membrane. AICAR, an activator of mitochondrial fatty acid oxidation (FAO), significantly reduced ACLY depletion‐mediated TG accumulation. These data indicate that inhibition of ACLY might affect both fatty acid elongation in ER and FAO in mitochondria, thereby explaining the TG accumulation with altered fatty acid composition. This phenotype may be a hallmark of growth suppression mediated by ACLY inhibition.

TRIB1 Supports Prostate Tumorigenesis and Tumor-Propagating Cell Survival by Regulation of Endoplasmic Reticulum Chaperone Expression

Endocrine therapy is the standard treatment for advanced prostate cancer; however, relapse occurs in most patients with few treatment options available after recurrence. To overcome this therapeutic hurdle, the identification of new molecular targets is a critical issue. The capability to proliferate in three-dimensional (3D) conditions is a characteristic property of cancer cells. Therefore, factors that regulate 3D growth are considered rational targets for cancer therapy. Here, we applied a functional genomic approach to the 3D spheroid cell culture model and identified TRIB1, a member of the Trib family of serine/threonine kinase-like proteins, as an essential factor for prostate cancer cell growth and survival. RNAi-mediated silencing of TRIB1 suppressed prostate cancer cell growth selectively under the 3D conditions. This effect was rescued by ectopic expression of an RNAi-resistant TRIB1 exogene. Gene signature-based analysis revealed that TRIB1 was related to endoplasmic reticulum (ER) pathways in prostate cancer and was required for expression of the ER chaperone GRP78, which is critical for prostate tumorigenesis. Of note, GRP78 was expressed preferentially in a subpopulation of prostate cancer cells that possess tumor-propagating potential, and these tumor-propagating cells were highly sensitive to TRIB1 and GRP78 depletion. In a xenograft model of human prostate cancer, TRIB1 depletion strongly inhibited tumor formation. Supporting these observations, we documented frequent overexpression of TRIB1 in clinical specimens of prostate cancer. Overall, our results indicated that the TRIB1-ER chaperone axis drives prostate tumorigenesis and the survival of the tumor-propagating cells.

Multicentric papillary renal cell carcinoma associated with renal adenomatosis

A case of multicentric papillary renal cell carcinoma (RCC) associated with renal adenomatosis in the bilateral kidneys is reported. Bilateral multiple renal cysts in a 46‐year‐old man were pointed out incidentally by ultrasonography. Some of the left renal lesions were considered to be RCC, and left radical nephrectomy was performed accordingly. The left kidney was occupied by numerous solid nodules, which ranged from yellow to tan in color, and some of the large ones had foci of hemorrhage and necrosis. Microscopically, most of the tumors showed papillary RCC associated with renal adenoma, while others consisted only of adenomas. Ten months later, multiple lesions of the right kidney, which were initially considered to be multiple cysts, were found to have become enlarged and some of them were diagnosed as RCC. Thus, right radical nephrectomy was also performed, and these tumors showed the same features as the left renal tumors. The patients familial history was not remarkable. The kidneys revealed various histological features, ranging from dysplastic to adenoma or carcinoma, including transitional or overlapping features between them. The findings suggest an adenoma‐carcinoma sequence in papillary RCC. It is worth considering such entities.