Role of NPHS Gene in Mammalian Myogenesis and Rhabdomyosarcoma

Rhabdomyosarcoma (RMS), the most common childhood soft tissue sarcoma, is a malignancy of muscle-lineage myoblasts that are blocked from differentiating into syncytial muscle. Treatments for high-risk RMS have not improved for three decades, underscoring the need to elucidate the molecular underpinnings of the disease and design new precision drug therapies. Using complementary model systems, the lab has uncovered misregulated myoblast cell-cell fusion signaling as a driver of RMS. As the machinery necessary for mammalian myoblast fusion is largely unknown, the lab has been probing for the myoblast cell membrane elements that facilitate RMS pathogenesis. We have generated preliminary data pointing towards Immunoglobulin Superfamily transmembrane Receptors (Ig-S-R) family members KIRREL and NPHS as putative fusion regulators, expression for which appears altered in RMS. To further probe for Ig-S-R activity in myoblast fusion and RMS, we considered the following: (1) If KIRREL and/or NPHS orchestrate myoblast fusion, we hypothesize that myoblasts, when switched to Differentiation Medium, should express either or both of the Ig-S-Rs; (2) When RMS cells are reprogrammed in culture to undergo differentiation and fusion, we predict that misexpression of these Ig-S-Rs are restored to comparably normal patterns. To address (1), we have used qRT-PCR to profile Kirrel and NPHS in differentiating wild-type myoblasts, which showed that Kirrel and NPHS are expressed and regulated during the window that fusion occurs. We are now utilizing shRNA against NPHS, as well as generating NPHS-overexpressing myoblast cell lines, to test whether NPHS is essential for myoblast differentiation and fusion, or can interfere with fusion when misregulated. To address (2), the lab has turned to All-trans retinoic acid (ATRA), which is known to reprogram the RMS RD cell line to undergo terminal differentiation. To determine whether Ig-S-R expression is altered in ATRA-induced reprogramming of RMS myoblasts, the lab used immunoblot analysis to show that expression of NPHS in ATRA-treated RD cells is properly restored. These results suggest that dysregulated NPHS expression associates with RMS. We are now testing genetically modified RMS cell lines to further profile how Ig-S-R misexpression facilitates RMS. In summary, our ongoing studies argue for Ig-S-R orthologs as RMS pathogenesis underpinnings, findings that will be presented and discussed at the Medical Student Research Forum.