CD44 alternative splicing and hnRNP A1 expression are associated with the metastasis of breast cancer

Abstract

Abstract. CD44 is a transmembrane receptor for hyaluronic acid. CD44 pre-mRNA contains 19 exons, 9 of which are alternatively spliced. Among the CD44 spliced variants, the v4-7 variant, one of the v6 exon-containing isoforms that contains variable exon 4, 5, 6 and 7, confers metastatic potential to nonmetastatic cells. Splicing of CD44 and the function of CD44 isoforms are different in breast cancer cells. hnRNP A1 is a ubiquitously expressed protein with an inhibitory function in pre-mRNA splicing. We showed that CD44v6 isoform, which includes all of the v6-containing mRNA isoforms, had the highest expression level in non-metatatic breast cancer cells (MCF7) when compared to the level in metastatic breast cancer cells (MDA-MB-231) and normal breast cells (MCF10A). Furthermore we showed that hnRNP A1 knockdown regulated splicing of CD44 differently in breast cancer cells. We showed here that CD44 isoform expression is completely different in MDA-MB-231 cells than that in MCF7 and MCF10A cells, whereas MCF7 and MCF10A cells had a similar expression pattern of CD44 isoforms. RT-PCR analysis of CD44v6 showed that MCF7 and MCF10A cells predominantly expressed the c5v6v7v8v9v10c6 isoform. However, in addition to this isoform, MDA-MB-231 cells also expressed the c5v6v8v9v10c6 and c5v6c6 isoforms. We also found that knockdown of hnRNP A1 significantly reduced the expression of c5v6v7v8v9v10c6 and c5v6v8v9v10c6, and promoted the expression of c5v6c6. hnRNP A1 knockdown significantly induced cell death. In addition, hnRNP A1 knockdown induced a decrease in cell invasion in the MDA-MB-231 cells. Our results indicate that the knockdown of hnRNP A1 has a specific function on the splicing of CD44 in breast cancer cells.

HnRNPM and CD44s expression affects tumor aggressiveness and predicts poor prognosis in breast cancer with axillary lymph node metastases

“…Moreover, it is well known that hnRNPs play a critical role in pre‐mRNA splicing and hnRNPA, L, and M 11 may regulate splicing of CD44 variants. CD44 alternative splicing is differentially regulated by hnRNPM during EMT, resulting in a switch in expression from the variable exon‐containing CD44v isoforms to the standard isoform, CD44s.…”

“…The existence of these different isoforms increases the heterogeneity of the CD44 protein products and there are discrepancies in the literature about the roles of CD44v and CD44s in tumor progression. [17][18][19] Moreover, it is well known that hnRNPs play a critical role in pre-mRNA splicing and hnRNPA, [20][21][22] L, and M 11 may regulate splicing of CD44 variants. CD44 alternative splicing is differentially regulated by hnRNPM during EMT, resulting in a switch in expression from the variable exon-containing CD44v isoforms to the standard isoform, CD44s.…”

α3-Deletion Isoform of HLA-A11 Modulates Cytotoxicity of NK Cells: Correlations with HIV-1 Infection of Cells

“…Recent studies have indicated that .95% of human genes undergo alternative splicing and that many point mutations that result in human genetic disease have disrupted splicing (38,39). Moreover, many immunologically relevant genes have been observed to undergo alternative splicing (40)(41)(42)(43). The present study includes four major findings.…”

Regulation of CD44 expression and focal adhesion by Golgi phosphatidylinositol 4‐phosphate in breast cancer

“…(23) Among these variants, the expression of CD44v6-10 is much higher than other variants in MCF7 cells. (24) Semiquantitative PCR showed that, among these variants, the expression of CD44s and CD44v mRNA was increased by SAC1 knockdown in MCF7 ( Fig. 1b) and SK-BR-3, another luminal-type, HER-2-enriched breast cancer cell (Fig.…”

“…Although MCF7 cells predominantly express CD44s, CD44 variants, including CD44v6‐10, v2‐10, and v3‐10, are also expressed . Among these variants, the expression of CD44v6‐10 is much higher than other variants in MCF7 cells . Semiquantitative PCR showed that, among these variants, the expression of CD44s and CD44v mRNA was increased by SAC1 knockdown in MCF7 (Fig.…”