Compensatory expression regulation of highly homologous proteins HNRNPA1 and HNRNPA2

Heterogeneous nuclear ribonucleoprotein (HNRNP) A1 and A2 are the most abundant HNRNPs with nearly identicalfunctions, and play important roles in regulating gene expression at multiple levels (i.e. transcription, posttranscription, and translation).However, the expression and regulation mechanism of HNRNPA1 and A2 themselves remain unclear. In this study, the amino acidsequences of HNRNPA1 and HNRNPA2 were compared and found to have 78% and 86% homology in key functional domains.Transfection of HEK293 cells with small interfering RNA and overexpression vectors of HNRNPA1 and HNRNPA2 demonstrated thatHNRNPA1 and HNRNPA2 paralogs regulate each other’s expression in a compensatory manner at both the RNA and protein levels.Multiprimer reverse transcription-polymerase chain reaction showed that HNRNPA1 and HNRNPA2 did not affect splicing of theHNRNPA2 and HNRNPA1 gene. Using luciferase reporting system, we found that compensatory degradation was mediated by the3′UTR of the two genes rather than by the promoter. Moreover, treatment with cycloheximide inhibited the compensatory regulation.Our results indicate a novel regulation mechanism of HNRNPA1 and A2 expression. Through compensatory regulation, the expressionlevels of HNRNPA1 and HNRNPA2 are strictly controlled within a certain range to maintain normal cellular activities under differentphysiological conditions.

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