Phosphoproteomic analysis reveals Smarcb1 dependent EGFR signaling in Malignant Rhabdoid tumor cells

Jonatan Darr, Agnes Klochendler, Sara Isaac, Tami Geiger, Amir Eden

The SWI/SNF ATP dependent chromatin remodeling complex is a multi-subunit complex, conserved in eukaryotic evolution that facilitates nucleosomal re-positioning relative to the DNA sequence. In recent years the SWI/SNF complex has emerged to play a role in cancer development as various sub-units of the complex are found to be mutated in a variety of tumors. One core-subunit of the complex, which has been well established as a tumor suppressor gene is SMARCB1 (SNF5/INI1/BAF47). Mutation and inactivation of SMARCB1 have been identified as the underlying mechanism leading to Malignant Rhabdoid Tumors (MRT) and Atypical Teratoid/Rhabdoid Tumors (AT/RT), two highly aggressive forms of pediatric neoplasms. We present a phosphoproteomic study of Smarcb1 dependent changes in signaling networks. The SILAC (Stable Isotopic Labeling of Amino Acids in Cell Culture) protocol was used to quantify in an unbiased manner any changes in the phosphoproteomic profile of Smarcb1 deficient murine rhabdoid tumor cell lines following Smarcb1 stable re-expression and under different serum conditions. This study illustrates broad changes in the regulation of multiple biological networks including cell cycle progression, chromatin remodeling, cytoskeletal regulation and focal adhesion. Specifically, we identify Smarcb1 dependent changes in phosphorylation and expression of the EGF receptor, demonstrate downstream signaling and show that inhibition of EGFR signaling specifically hinders the proliferation of Smarcb1 deficient cells. These results support recent findings regarding the effectivity of EGFR inhibitors in hindering the proliferation of human MRT cells and demonstrate that activation of EGFR signaling in Rhabdoid tumors is SMARCB1 dependent.