6597

SMARCA4

BAF190|BRG1|RTPS2|SNF2|SNF2-BETA|SNF2L4|SNF2LB|SWI2|hSNF2b;SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily a, member 4;SMARCA4;SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily a, member 4

ATP-dependent helicase SMARCA4|BAF190A|BRG1-associated factor 190A|BRM/SWI2-related gene 1|SNF2-like 4|SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily A member 4|brahma protein-like 1|global transcription activator homol

19p13.2

protein-coding

Count: 1; Generif

microRNA-21 (miR-21) is a key regulator of oncogenic processes. It is significantly elevated in the majority of human tumors and functionally linked to cellular proliferation, survival and migration. In this study, we used two experimental-based strategies to search for novel miR-21 targets. On the one hand, we performed a proteomic approach using two-dimensional differential gel electrophoresis (2D-DIGE) to identify proteins suppressed upon enhanced miR-21 expression in LNCaP human prostate carcinoma cells. The tumor suppressor acidic nuclear phosphoprotein 32 family, member A (ANP32A) (alias pp32 or LANP) emerged as the most strongly downregulated protein. On the other hand, we applied a mathematical approach to select correlated gene sets that are negatively correlated with primary-miR-21 (pri-miR-21) expression in published transcriptome data from 114 B-cell lymphoma cases. Among these candidates, we found tumor suppressor SMARCA4 (alias BRG1) together with the already validated miR-21 target, PDCD4. ANP32A and SMARCA4, which are both involved in chromatin remodeling processes, were confirmed as direct miR-21 targets by immunoblot analysis and reporter gene assays. Furthermore, knock down of ANP32A mimicked the effect of enforced miR-21 expression by enhancing LNCaP cell viability, whereas overexpression of ANP32A in the presence of high miR-21 levels abrogated the miR-21-mediated effect. In A172 glioblastoma cells, enhanced ANP32A expression compensated for the effects of anti-miR-21 treatment on cell viability and apoptosis. In addition, miR-21 expression clearly increased the invasiveness of LNCaP cells, an effect also seen in part upon downregulation of ANP32A. In conclusion, these results suggest that downregulation of ANP32A contributes to the oncogenic function of miR-21.

Components of the SWI/SNF chromatin-remodeling complex, such as INI1, are inactivated in human cancer and, thus, act as tumor suppressors. Here we screened for mutations the entire coding sequence of BRG1 (SMARCA4), which encodes the ATPase of the complex, in 59 lung cancer cell lines of the most common histopathological types. mutations were detected in 24% of the cancer cell lines, many of them in cells commonly used for lung cancer research. All mutations were homozygous and most predicted truncated proteins. The alterations were significantly more frequent in the non-small-cell lung cancer (NSCLC) type (13/37, 35%) as compared to the small-cell lung cancer (SCLC) type (1/19, 5%) (P<0.05; Fisher's Exact test) and BRG1 was the fourth most frequently altered gene in NSCLC cell lines. BRG1 mutations coexisted with mutations/deletions at KRAS, LKB1, NRAS, P16, and P53. However, alterations at BRG1 always occurred in the absence of MYC amplification, suggesting a common role in lung cancer development. In conclusion, our data strongly support that BRG1 is a bona fide tumor suppressor and a major factor in lung tumorigenesis.

Components of the SWI/SNF chromatin-remodeling complex, such as INI1, are inactivated in human cancer and, thus, act as tumor suppressors. Here we screened for mutations the entire coding sequence of BRG1 (SMARCA4), which encodes the ATPase of the complex, in 59 lung cancer cell lines of the most common histopathological types. mutations were detected in 24% of the cancer cell lines, many of them in cells commonly used for lung cancer research. All mutations were homozygous and most predicted truncated proteins. The alterations were significantly more frequent in the non-small-cell lung cancer (NSCLC) type (13/37, 35%) as compared to the small-cell lung cancer (SCLC) type (1/19, 5%) (P<0.05; Fisher's Exact test) and BRG1 was the fourth most frequently altered gene in NSCLC cell lines. BRG1 mutations coexisted with mutations/deletions at KRAS, LKB1, NRAS, P16, and P53. However, alterations at BRG1 always occurred in the absence of MYC amplification, suggesting a common role in lung cancer development. In conclusion, our data strongly support that BRG1 is a bona fide tumor suppressor and a major factor in lung tumorigenesis.

A role for the SWI/SNF complex in tumorigenesis based on its requirement for retinoblastoma induced growth arrest and p53-mediated transcription and the appearance of tumors in SWI/SNF-deficient mice. In addition, Western blot data have shown that the SWI/SNF ATPase subunits cell, BRG1 and BRM (BRG1/BRM), are lost in approximately 30% of human non-small lung cancer cell lines. To determine whether loss of expression of these proteins occurs in primary tumors, we examined their expression in 41 primary lung adenocarcinomas and 19 primary lung squamous carcinomas by immunohistochemistry. These analyses showed that 10% of tumors show a concomitant loss of BRG1 and BRM expression. Moreover, patients with BRG1/BRM-negative carcinomas, independent of stage, have a statistically significant decrease in survival compared with patients with BRG1/BRM. This report provides supportive evidence that BRG1 and BRM act as tumor suppressor proteins and implicates a role for their loss in the development of non-small cell lung cancers.