Novel nuclear RNA export factor 1 adaptor drives tumor growth by increasing proliferation-stimulatory mRNA export

mRNA nuclear export is an essential biological process that is mediated primarily by nuclear export factor 1 (NXF1). NXF1 exerts its mRNA transport activity by binding to adaptor proteins. In an effort to identify novel NXF1 adaptors involved in hepatocellular carcinoma (HCC) development, we discovered that C7orf25, a previously uncharacterized protein named proliferation-associated NXF1 adaptor (PANAD), interacts with NXF1 in the nucleus. Specifically, the R122/E125/G133/D139 residues of PANAD bound to the Q20/K22/K23 residues in the RBD of NXF1. This binding disrupted the intramolecular interaction between the RBD and NTF2L domains of NXF1, thereby enhancing the association of NXF1 with target mRNAs. The mRNAs whose nuclear export was impaired upon PANAD knockdown were highly enriched in cell proliferation pathways. Moreover, PANAD directly bound to CDK6 mRNA. Gain- and loss-of-function analyses in cellular and mouse models revealed that PANAD accelerated G1/S transition and tumor cell proliferation, promoted colony formation and hepatoma xenograft growth, and acted through interactions with NXF1 to increase the nuclear export and translation of mRNAs encoding proliferation stimulators, including CDK6. PANAD and CDK6 were both upregulated in HCC tissues and were positively correlated. Furthermore, PANAD-overexpressing hepatoma cells exhibited increased sensitivity to the CDK4/6 inhibitor palbociclib, whereas PANAD-silenced cells exhibited reduced sensitivity. These findings identify PANAD as a novel NXF1 adaptor; delineate its critical regulatory roles in mRNA nuclear export, G1/S transition and tumor development; and highlight its potential as both a therapeutic target and a predictive biomarker for CDK4/6-targeted therapy.