Context-dependent modulation of aggressiveness of pediatric tumors by individual oncogenic RAS isoforms

Abstract

A prototypic pediatric cancer that frequently shows activation of RAS signaling is embryonal rhabdomyosarcoma (ERMS). ERMS also show aberrant Hedgehog (HH)/GLI signaling activity and can be driven by germline mutations in this pathway. We show, that in ERMS cell lines derived from sporadic tumors i.e. from tumors not caused by an inherited genetic variant, HH/GLI signaling plays a subordinate role, because oncogenic mutations in HRAS, KRAS, or NRAS (collectively named oncRAS) inhibit the main HH target GLI1 via the MEK/ERK-axis, but simultaneously increase proliferation and tumorigenicity. oncRAS also modulate expression of stem cell markers in an isoform- and context-dependent manner. In Hh-driven murine ERMS that are caused by a Patched mutation, oncHRAS and mainly oncKRAS accelerate tumor development, whereas oncNRAS induces a more differentiated phenotype. These features occur when the oncRAS mutations are induced at the ERMS precursor stage, but not when induced in already established tumors. Moreover, in contrast to what is seen in human cell lines, oncRAS mutations do not alter Hh signaling activity and marginally affect expression of stem cell markers. Together, all three oncRAS mutations seem to be advantageous for ERMS cell lines despite inhibition of HH signaling and isoform-specific modulation of stem cell markers. In contrast, oncRAS mutations do not inhibit Hh-signaling in Hh-driven ERMS. In this model, oncRAS mutations seem to be advantageous for specific ERMS populations that occur within a specific time window during ERMS development. In addition, this window may be different for individual oncRAS isoforms, at least in the mouse.

Oncogenic NRAS Accelerates Rhabdomyosarcoma Formation When Occurring within a Specific Time Frame during Tumor Development in Mice

“…As described above, we recently generated Ptch +/mice that harbor a conditional oncogenic NRasG12D (NRas fl ) allele [12]. To activate the expression of oncNRAS in ERMS of Ptch +/-NRas fl/+ mice, the animals were bred to Myf5 CreER mice that express a tamoxifeninducible Cre recombinase in Myf5-expressing cells [12,13].…”

“…As described above, we recently generated Ptch +/mice that harbor a conditional oncogenic NRasG12D (NRas fl ) allele [12]. To activate the expression of oncNRAS in ERMS of Ptch +/-NRas fl/+ mice, the animals were bred to Myf5 CreER mice that express a tamoxifeninducible Cre recombinase in Myf5-expressing cells [12,13]. Using this model, we showed that induction of oncNRAS in 4-week-old Ptch +/mice does not influence incidence, growth or proliferation of the tumors when compared to the controls [12] (summarized in Table 1).…”

“…Our data show that none of the oncRAS isoforms affect ERMS growth when induced at the full-blown, palpable tumor stage. In contrast, when induced at the tumor precursor stage at 4 weeks of age, oncKRAS and oncHRAS mutations reinforce tumor development, whereas oncNRAS does not and rather induces a more differentiated phenotype [12].…”

The hidden hedgehog of the pituitary: hedgehog signaling in development, adulthood and disease of the hypothalamic-pituitary axis

“…MEK or MAP2K) ( 48 – 52 ). Furthermore, oncogenic RAS can – dependent on the cancer entity – also inhibit GLI via MEK and/or ERK (extracellular signal-regulated kinase) ( 53 , 54 ). Additionally, WNT signaling is able to interfere with GLI signal transduction.…”

Genetic Characterization, Current Model Systems and Prognostic Stratification in PAX Fusion-Negative vs. PAX Fusion-Positive Rhabdomyosarcoma

“…Further, SHH seems to control self-renewal of FN-RMS; its inhibition has been shown to reduce chemotherapy resistance [69]. In addition, there is new evidence that oncogenic RAS mutations (HRAS, KRAS and NRAS) inhibit GLI1 via the MEK/ERK pathway but concurrently lead to increased proliferation and oncogenicity [70].…”