Figure 2: Functions of hnRNP A/B family in SMC differentiation. hnRNP A2/B1 and hnRNP A1 seem to regulate SMC specific gene expression and cell differentiation at two transcriptional levels. hnRNP A2/B1 or hnRNP A1 activates or modulates the transcriptional machinery of SMC specific genes by upregulating another SMC differentiation mediator, Cbx3, or SMC transcription factors and/or co-activators such as SRF, myocardin, and MEF2c, respectively, resulting in SMC differentiation gene expression. hnRNP A1 or hnRNP A2/B1 can also directly regulate SMC differentiation gene expression through SRF binding elements or other specific binding sites within SMC specific gene promoter region.