Expression of pericyte, mesangium and muscle markers in malignant rhabdoid tumor cell lines: Differentiation‐induction using 5‐azacytidine

Malignant rhabdoid tumor (MRT) has been considered to have multiphenotypic diversity characteristics. Some MRTs exhibit a neural phenotype. However, it is still unclear whether MRT cells can display a skeletal muscle, smooth muscle or smooth muscle‐like cell phenotype, like those of pericytes and mesangial cells. To determine if MRTs exhibit skeletal muscle cell or smooth muscle‐like cell phenotypes, six MRT cell lines (TM87‐16, STM91‐01, TTC549, TTC642, YAM‐RTK1 and TTC1240) were examined for markers of skeletal muscle (MyoD, myogenin, myf‐5, myf‐6, acetylcholine receptor‐α, ‐β and ‐γ), smooth muscle (α‐smooth muscle actin, SM‐1 and SM22), and smooth muscle‐like cells, such as pericytes (angiopoietin‐1 and ‐2) and mesangial cells (megsin), using conventional RT‐PCR, semi‐quantitative PCR, western blotting and immunocytochemistry before and after differentiation‐induction with 5‐azacytidine. α‐Smooth muscle actin and SM22 were detected in all six MRT cell lines, while MyoD and myf‐5, crucial markers for skeletal myogenic determination, were not. The TM87‐16 cell line expressed SM‐1 and angiopoietin‐1. TTC1240 also expressed angiopoietin‐1. Interestingly, STM91‐01 expressed megsin, a novel marker for mesangial cells, in addition to angiopoietin‐1. Our results indicated that some MRTs exhibited smooth muscle and/or smooth muscle‐like cell phenotypes and some renal MRTs might be of mesangial origin. Recently, smooth muscle and also smooth muscle‐like cells have been considered to be of neuroectodermal origin. MRT can thus considered to belong to the category of primitive neuroectodermal tumors (PNETs) in the broad sense.