Human fibroblast growth factor 9 (FGF9) is a potent mitogen involved in many physiological processes. Although FGF9 messenger RNA (mRNA) is ubiquitously expressed in embryos, FGF9 protein expression is generally low and restricted to a few adult organs. Aberrant expression of FGF9 usually results in human malignancies including cancers, but the mechanism remains largely unknown. Here, we report that FGF9 protein, but not mRNA, was increased in hypoxia. Two sequence elements, the upstream open reading frame (uORF) and the internal ribosome entry site (IRES), were identified in the 5' UTR of FGF9 mRNA. Functional assays indicated that FGF9 protein synthesis was normally controlled by uORF-mediated translational repression, which kept the protein at a low level, but was upregulated in response to hypoxia through a switch to IRES-dependent translational control. Our data demonstrate that FGF9 IRES functions as a cellular switch to turn FGF9 protein synthesis ‘on’ during hypoxia, a likely mechanism underlying FGF9 overexpression in cancer cells. Finally, we provide evidence to show that hypoxia-induced translational activation promotes FGF9 protein expression in colon cancer cells. Altogether, this dynamic working model may provide a new direction in anti-tumor therapies and cancer intervention.

Background Hypoxia suppresses global protein production, yet certain essential proteins are translated through alternative pathways to survive under hypoxic stress. Translation via the internal ribosome entry site (IRES) is a means to produce proteins under stress conditions such as hypoxia; however, the underlying mechanism remains largely uncharacterized. Methods Proteomic and bioinformatic analyses were employed to identify hnRNPM as an IRES interacting factor. Clinical specimens and mouse model of tumorigenesis were used for determining the expression and correlation of hnRNPM and its target gene. Transcriptomic and translatomic analyses were performed to profile target genes regulated by hnRNPM. Findings Hypoxia increases cytosolic hnRNPM binding onto its target mRNAs and promotes translation initiation. Clinical colon cancer specimens and mouse carcinogenesis model showed that hnRNPM is elevated during the development of colorectal cancer, and is associated with poor prognosis. Genome-wide transcriptomics and translatomics analyses revealed a unique set of hnRNPM-targeted genes involved in metabolic processes and cancer neoplasia are selectively translated under hypoxia. Interpretation These data highlight the critical role of hnRNPM-IRES-mediated translation in transforming hypoxia-induced proteome toward malignancy. Fund This work was supported by the Ministry of Science and Technology, Taiwan (MOST 104–2320-B-006-042 to HSS and MOST 105–2628-B-001-MY3 to TMC).

Intratumoral heterogeneity (ITH) can promote cancer progression and treatment failure, but the complexity of the regulatory programs and contextual factors involved complicates its study. To understand the specific contribution of ITH to immune checkpoint blockade (ICB) response, we generated single cell-derived clonal sublines from an ICB-sensitive and genetically and phenotypically heterogeneous mouse melanoma model, M4. Genomic and single cell transcriptomic analyses uncovered the diversity of the sublines and evidenced their plasticity. Moreover, a wide range of tumor growth kinetics were observed in vivo, in part associated with mutational profiles and dependent on T cell-response. Further inquiry into melanoma differentiation states and tumor microenvironment (TME) subtypes of untreated tumors from the clonal sublines demonstrated correlations between highly inflamed and differentiated phenotypes with the response to anti-CTLA-4 treatment. Our results demonstrate that M4 sublines generate intratumoral heterogeneity at both levels of intrinsic differentiation status and extrinsic TME profiles, thereby impacting tumor evolution during therapeutic treatment. These clonal sublines proved to be a valuable resource to study the complex determinants of response to ICB, and specifically the role of melanoma plasticity in immune evasion mechanisms.