Rhabdomyosarcoma is the most common pediatric soft-tissue sarcoma, which includes two major subtypes, alveolar and embryonal rhabdomyosarcoma. The mechanism of its oncogenesis is largely unknown. However, the oncogenic process of rhabdomyosarcoma involves multi-stages of signaling protein dysregulation characterized by prolonged activation of tyrosine and serine/threonine kinases. To better understand this protein dysregulation, we evaluated the phosphorylation profiles of multiple tyrosine and serine/threonine kinases to identify whether these protein kinases are activated in rhabdomyosarcoma. We applied immunohistochemistry with phospho-specific antibodies to examine phosphorylation levels of selected receptor and non-receptor tyrosine kinases, mammalian target of rapamycin (mTOR), p70S6K, and protein kinase C (PKC) isozymes on alveolar and embryonal rhabdomyosarcoma tissue microarray slides. Our results showed that the phosphorylation levels of these kinases are elevated in some rhabdomyosarcoma tissues compared to normal tissues. Phosphorylation levels of receptor and non-receptor tyrosine kinases are elevated between 26 and 68% in alveolar rhabdomyosarcoma and between 24 and 71% in embryonal rhabdomyosarcoma, respectively, compared to normal tissues. In addition, phosphorylation levels of mTOR and its downstream targets, p70S6K, S6, and 4EBP1, are increased between 50 and 72% in both subtypes of rhabdomyosarcoma. Further, phosphorylation levels of PKCa, PKCd, PKCh, and PKCf/k are upregulated between 57 and 69% in alveolar rhabdomyosarcoma and between 43 and 72% in embryonal rhabdomyosarcoma. This is the first report to create a phosphorylation profile of tyrosine and serine/threonine kinases involved in the mTOR and PKC pathways of alveolar and embryonal rhabdomyosarcoma. These protein kinases may play roles in the development or tumor progression of rhabdomyosarcomas and thus may serve as novel targets for therapeutic intervention. Most of these tumors arise in the head and neck region, genitourinary tract, and extremities. The two main histological subtypes of rhabdomyosarcoma are embryonal rhabdomyosarcoma, which comprises more than half of all rhabdomyosarcoma cases, and alveolar rhabdomyosarcoma, which is less common but more aggressive. These two subtypes arise at different primary body sites and have different age patterns.2 Clinically, the presentation of rhabdomyosarcoma is genetically heterogeneous. However, some genetic markers have been identified. Among them, approximately 75% of alveolar rhabdomyosarcoma are characterized by chromosomal translocation, most frequently, t(2;13)(q35;q14) or the variant t(1;13)(q36;q14).
3These translocations can disrupt either the PAX3
