MMSA-1 is regulated by Wnt/TCF4 and involved in multiple myeloma progression and invasion via RAS/RAF signaling pathway

As a novel multiple myeloma (MM) specific antigen, rare is known about the underlying molecular mechanism of MMSA-1 gene in the progression of myeloma. Transcription factor 4 (TCF4) and MMSA-1 over/down expressed stable U266 cell lines was constructed using lentivirus transfection technique. TCF4's impact on MMSA-1 expression was explored. Overexpressed of MMSA-1's interaction with RAS protein and its downstream signaling pathways was investigated. Moreover, the interaction changes between overexpressed MMSA-1 protein and bone marrow microenvironment were also detected by examing adhesion molecules and angiogenesis promoting factors using Western Blot. We successfully constructed transcription factor 4 (TCF4) and MMSA-1 over/down expressed stable U266 cell lines (termed ^TCF4-/+U266 and ^MMSA-1-/+U266). Our result showed that TCF4 could bind with MMSA-1 promoter sequence, greatly up regulate its promotor activity and then improve MMSA-1 expression. Overexpressed MMSA-1 also made a series of changes in U266 cells, including promoting RAS protein expression in cytoplasm, enhancing the interaction between MMSA-1 and RAS, which resulted in hyperactivation of RAS and its downstream signaling pathways including RAF/MEK/ERK and RAF/PI3K/AKT, improving U266 cells' clonogenicity capacity, changing apoptosis related proteins, reducing the interaction between myeloma cell and bone marrow microenvironment by reducing adhesion molecules expression including HIF-1α, E-cadherin, CXCR4 expression and elevating angiogenesis promoting factors including VEGF, Ang-2 and reducing Ang-1 at the same time. These results suggested MMSA-1 was over expressed in MM cells being regulated by Wnt/β-catenin/TCF4 signaling pathway, which resulted in hyperactivation of downstream RAS/RAF signaling pathway and eventually promote myeloma cells survival and invasion.