Functional Analysis of Alternative Isoforms of the Transcription Factor PAX3 in Melanocytes In vitro

Abstract

Transcription factor PAX3 has seven isoforms of which PAX3c has been studied extensively whereas the functions of the other isoforms are less well known. Here, we found that PAX3 isoforms in a stable transfection system have different biological functions in mouse melanocytes in vitro. PAX3a and PAX3b had negative effects on melanocyte proliferation but had no discernable effect on melanocyte growth in soft agar. PAX3a did not affect cell migration and apoptosis but PAX3b reduced migration and accelerated apoptosis. PAX3c and PAX3d promoted cell proliferation, migration, transformation, and survival. PAX3e reduced melanocyte growth; transformation and migration were unchanged and apoptosis was increased in vitro. PAX3g did not influence cell proliferation or apoptosis. Cells expressing PAX3g were able to grow in soft agar but migration was reduced. PAX3h increased cell proliferation, migration, survival, and transformation. These functional studies have advanced our understanding of the effects of PAX3 isoforms in melanocytes and their potential contribution in tumorigenesis. (Cancer Res 2006; 66(17): 8574-80)

Alternative Polyadenylation Mediates MicroRNA Regulation of Muscle Stem Cell Function

“…Three types of APA (I, II, and III) have been defined with regard to the location of the different PAS and whether the APA is coupled with an alternative splicing (Lutz, 2008; Millevoi and Vagner, 2010; Zhao et al, 1999; Edwalds-Gilbert et al, 1997). In human and mouse cells, Pax3 transcripts display a complex pattern of alternative splicing with at least eight different transcript variants reported (Barber et al, 1999; Pritchard et al, 2003; Wang et al, 2006; Parker et al, 2004). Considering the complex alternative splicing of Pax3 transcripts, it is likely that Pax3 APA falls into the type III category in which splicing events affect the 3′ end processing of Pax3 mRNA.…”

Alternate PAX3 and PAX7 C-terminal isoforms in myogenic differentiation and sarcomagenesis

“…These two transcripts in particular were shown to promote melanocyte proliferation, migration and survival [12]. In ARMS cell lines tested for the presence of PAX3 C-terminal isoforms, PAX3d was the predominant isoform in all cell lines, while PAX3c was strongly expressed but in about half of these cells [25].…”

“…Expression and functional activities of PAX3 C-terminal isoforms have only been studied in melanocytes and melanoma cell lines [11,12]. To date, it is unknown which isoforms are predominantly expressed in primary myoblasts, although it is suggested that all full-length isoforms are involved in myoblast development [13].…”

BRAF activates PAX3 to control muscle precursor cell migration during forelimb muscle development

“…It is also known that PAX3 controls expression of Met in the ventro-lateral dermomyotome (Relaix et al, 2005; Yang et al, 1996) by direct binding to the Met gene promoter (Epstein et al, 1996), thereby enabling delamination and migration of limb muscle precursor cells. However, the full complexity of the interactions within the genetic network orchestrating limb muscle precursor cell migration and the functional regulation of the activity of PAX3 and its multiple isoforms (Wang et al, 2006) has not been uncovered yet.…”