Progression and Differentiation of Alveolar Rhabdomyosarcoma Is Regulated by PAX7 Transcription Factor—Significance of Tumor Subclones

Abstract

Rhabdomyosarcoma (RMS), is the most frequent soft tissue tumor in children that originates from disturbances in differentiation process. Mechanisms leading to the development of RMS are still poorly understood. Therefore, by analysis of two RMS RH30 cell line subclones, one subclone PAX7 negative, while the second one PAX7 positive, and comparison with other RMS cell lines we aimed at identifying new mechanisms crucial for RMS progression. RH30 subclones were characterized by the same STR profile, but different morphology, rate of proliferation, migration activity and chemotactic abilities in vitro, as well as differences in tumor morphology and growth in vivo. Our analysis indicated a different level of expression of adhesion molecules (e.g., from VLA and ICAM families), myogenic microRNAs, such as miR-206 and transcription factors, such as MYOD, MYOG, SIX1, and ID. Silencing of PAX7 transcription factor with siRNA confirmed the crucial role of PAX7 transcription factor in proliferation, differentiation and migration of RMS cells. To conclude, our results suggest that tumor cell lines with the same STR profile can produce subclones that differ in many features and indicate crucial roles of PAX7 and ID proteins in the development of RMS.

Non-coding RNA in rhabdomyosarcoma progression and metastasis

“…MiR-1/miR-206 expression may also be regulated by PAX transcription factors. This is demonstrated by the fact that in FP-RMS Rh30 cell line, subclones lacking the expression of transcription factor PAX7 displayed decreased proliferation and migration accompanied with enhanced expression of several myomiR including miR-1-3p, miR-133a-3p, miR-133b, and miR-206 compared to PAX7-positive cells ( 93 ). SiRNA-mediated silencing of PAX7 in the latter led to increased expression of these myomiR.…”

Current Thoughts of Notch’s Role in Myoblast Regulation and Muscle-Associated Disease

“…In this overexpressed Notch model, there was a 3–4-fold decrease in MyoD and myogenin [ 36 ]. The data suggest that Notch’s activation of Pax7 caused Pax7 to inhibit differentiation by either activating DNA binding and differentiation (ID) proteins (Id2 and Id3) to MyoD or activating proteasome-dependent MyoD [ 39 , 44 , 45 ]. Silenced PAX7 expression with siRNA in rhabdomyosarcoma cell line RH30 PAX7 + cells led to decreased proliferation of the factors ID1, -2, -3, and -4 and sine oculis-related homeobox (SIX1 and -4) but increased MyoD and MyoG [ 39 ].…”

“…The data suggest that Notch’s activation of Pax7 caused Pax7 to inhibit differentiation by either activating DNA binding and differentiation (ID) proteins (Id2 and Id3) to MyoD or activating proteasome-dependent MyoD [ 39 , 44 , 45 ]. Silenced PAX7 expression with siRNA in rhabdomyosarcoma cell line RH30 PAX7 + cells led to decreased proliferation of the factors ID1, -2, -3, and -4 and sine oculis-related homeobox (SIX1 and -4) but increased MyoD and MyoG [ 39 ]. How Pax7 directs ID’s inhibition of MyoD is not clear, but there is evidence that IDs bind to the MRFs’ E-proteins and prevent transcriptional activity [ 46 ].…”