Distinct and Overlapping Sarcoma Subtypes Initiated from Muscle Stem and Progenitor Cells

Abstract

SUMMARY Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children, while undifferentiated pleomorphic sarcoma (UPS) is one of the most common soft tissue sarcomas diagnosed in adults. To investigate the myogenic cell(s) of origin of these sarcomas, we used Pax7-CreER and MyoD-CreER mice to transform Pax7+ and MyoD+ myogenic progenitors by expressing oncogenic KrasG12D and deleting p53 in vivo. Pax7-CreER mice developed RMS and UPS, while MyoD-CreER mice developed UPS. Using gene set enrichment analysis, RMS and UPS each clustered specifically within their human counterparts. These results suggest that RMS and UPS have distinct and overlapping cells of origin within the muscle lineage. Taken together, we have established novel mouse models of soft tissue sarcoma from muscle stem and progenitor cells. SIGNIFICANCE Although muscle stem cells have been presumed to be a cell of origin for RMS, studies with constitutive Cre drivers expressed in Myf6-expressing cells or adipocyte P2-expressing cells suggest that cells of origin for RMS can be differentiated myofibers or adipogenic precursors, respectively. However, recent studies have demonstrated that Myf6 is expressed in muscle stem cell precursors, revealing a potential limitation of utilizing constitutive Cre drivers for cell of origin studies. Here, using inducible CreER mice, we mutate genes relevant to human RMS specifically in Pax7-expressing or MyoD-expressing cells. Our results suggest that RMS can be initiated in muscle stem cells, while UPS can be initiated in activated (Pax7+MyoD+) satellite cells.

Acute Tissue Injury Activates Satellite Cells and Promotes Sarcoma Formation via the HGF/c-MET Signaling Pathway

“…To study sarcoma development, we utilized Pax7 CreER/+ ; Kras LSL-G12D/+ ; Trp53 flox/flox (P7KP) mice because mutations in the Ras and p53 pathways have been reported in human soft tissue sarcoma (4, 5). Following systemic administration of tamoxifen by intraperitoneal (IP) injection, P7KP mice develop sarcomas throughout the animal in 6–8 weeks (6). The most common locations for sarcoma development are the body wall, extremities, and head and neck (6).…”

“…Following systemic administration of tamoxifen by intraperitoneal (IP) injection, P7KP mice develop sarcomas throughout the animal in 6–8 weeks (6). The most common locations for sarcoma development are the body wall, extremities, and head and neck (6). Similar to other reports, the histology of the sarcomas in P7KP mice exist along a continuum of undifferentiated pleomorphic sarcoma (UPS), myogenic UPS, and embryonal rhabdomyosarcoma (6, 7).…”

“…The most common locations for sarcoma development are the body wall, extremities, and head and neck (6). Similar to other reports, the histology of the sarcomas in P7KP mice exist along a continuum of undifferentiated pleomorphic sarcoma (UPS), myogenic UPS, and embryonal rhabdomyosarcoma (6, 7). To develop a temporally- and spatially-restricted model of STS, we injected P7KP mice with 4-hydroxytamoxifen (4OHT) directly into the gastrocnemius muscle.…”

Uncovering metabolism in rhabdomyosarcoma

“…21,22 Patients who have localized RMS have a 5-year survival greater than 70% following a multimodal approach that includes chemotherapy, radiation therapy, and surgery; yet, overall survival of patients with metastasis remains poor. 23,24 Cells mainly deriving from myogenic lineages have been shown to contribute to RMS development in mouse [25][26][27][28] and zebrafish models, 29 yet even nonmyogenic lineages could participate in the formation of RMS. 30 As a result, these tumors can arise in or near to skeletal muscle districts as well as in sites that lack skeletal muscle, such as the biliary and genitourinary tract.…”

A versatile modular vector system for rapid combinatorial mammalian genetics

“…We show that the combinations of oncogenic H-Ras G12V expression plus knockdown of Cdkn2a, Trp53, or both Trp53 and Pten cause the formation of undifferentiated sarcomas with pleomorphic and rhabdoid features from skeletal muscles in mice. The histological similarity of these tumor models to existing transgenic mouse muscle-derived sarcoma models that are driven by oncogenic K-Ras G12V in Trp53 null, Trp53 point mutant, or Cdkn2a null genetic backgrounds (27)(28)(29)(30) demonstrates that MuLE viruses can be employed to recapitulate transgenic tumor models. Interestingly, additional Pten knockdown in shRNA-Trp53 plus H-Ras G12V tumors caused phosphorylation of AKT, demonstrating hyperactivation of the PI3K pathway, but did not lead to any obvious differences in Cloning of sgRNAs, surveyor assays, and next generation sequencing.…”