Splicing program of human MEN A produces a previously undescribed isoform associated with invasive, mesenchymal-like breast tumors

摘要

Human mena (hMENA), a member of the actin cytoskeleton regulators Ena/VASP, is overexpressed in high-risk preneoplastic lesions and in primary breast tumors and has been identified as playing a role in invasiveness and poor prognosis in breast cancers that express HER2. Here we identify a unique isoform, hMENAAv6, derived from the hMENA alternative splicing program. In an isogenic model of human breast cancer progression, we show that hMENA~(11a) is expressed in premalignant cells, whereas hMENAAv6 expression is restricted to invasive cancer cells. "Reversion" of the malignant phe-notype leads to concurrent down-regulation of all hMENA isoforms. In breast cancer cell lines, isoform-specific hMENA overexpression or knockdown revealed that in the absence of hMENA~(11a), overexpression of hMENAAv6 increased cell invasion, whereas overexpression of hMENA~(11a) reduced the migratory and invasive ability of these cells. hMENA~(11a) splicing was shown to be dependent on the epithelial regulator of splicing 1 (ESRP1), and forced expression of ESRP1 in invasive mesenchymal breast cancer cells caused a phenotypic switch reminiscent of a mesenchymal-to-epithelial transition (MET) characterized by changes in the cytoskeletal architecture, reexpres-sion of hMENA~(11a), and a reduction in cell invasion. hMENA-positive primary breast tumors, which are hMENA~(11a)-negative, are more frequently E-cadherin low in comparison with tumors expressing hMENA~(11a). These data suggest that polarized and growth-arrested cellular architecture correlates with absence of alternative hMENA isoform expression, and that the hMENA splicing program is relevant to malignant progression in invasive disease.