Regulated gene expression is critical for the proper timing of cell cycle transitions. Here we report that human LIN-9 has an important function in transcriptional regulation of G2/M genes. Depletion of LIN-9 by RNAi in human fibroblasts strongly impairs proliferation and delays progression from G2 to M. We identify a cluster of G2/M genes as direct targets of LIN-9. Activation of these genes is linked to an association between LIN-9 and B-MYB. Chromatin immunoprecipitation assays revealed binding of both LIN-9 and B-MYB to the promoters of G2/M regulated genes. Depletion of B-MYB recapitulated the biological outcome of LIN-9 knockdown, including impaired proliferation and reduced expression of G2/M genes. These data suggest a critical role for human LIN-9, together with B-MYB, in the activation of genes that are essential for progression into mitosis.
Although common cancer hallmarks are well established, lineage-restricted oncogenes remain less understood. Here, we report an inherent dependency of melanoma cells on the small GTPase RAB7, identified within a lysosomal gene cluster that distinguishes this malignancy from over 35 tumor types. Analyses in human cells, clinical specimens, and mouse models demonstrated that RAB7 is an early-induced melanoma driver whose levels can be tuned to favor tumor invasion, ultimately defining metastatic risk. Importantly, RAB7 levels and function were independent of MITF, the best-characterized melanocyte lineage-specific transcription factor. Instead, we describe the neuroectodermal master modulator SOX10 and the oncogene MYC as RAB7 regulators. These results reveal a unique wiring of the lysosomal pathway that melanomas exploit to foster tumor progression.
Genetic studies in Caenorhabditis elegans identified lin-9 to function together with the retinoblastoma homologue lin-35 in vulva differentiation. We have now identified a human homologue of Lin-9 (hLin-9) and provide evidence about its function in the mammalian pRB pathway. hLin-9 binds to pRB and cooperates with pRB in flat cell formation in Saos-2 cells. In addition, hLin-9 synergized with pRB and Cbfal to transactivate an osteoblast-specific reporter gene. In contrast, hLin-9 was not involved in pRB-mediated inhibition of cell cycle progression or repression of E2F-dependent transactivation. Consistent with these data, hLin-9 was able to associate with partially penetrant pRB mutants that do not bind to E2F, but retain the ability to activate transcription and to promote differentiation. hLin-9 can also inhibit oncogenic transformation, dependent on the presence of a functional pRB protein. RNAi-mediated knockdown of Lin-9 can substitute for the loss of pRB in transformation of human primary fibroblasts. These data suggest that hLin-9 has tumor-suppressing activities and that the ability of hLin-9 to inhibit transformation is mediated through its association with pRB.
The flavin-binding BLUF domain functions as a blue-light receptor in eukaryotes and bacteria. In the photoreceptor protein photoactivated adenylyl cyclase (PAC) from the flagellate Euglena gracilis, the BLUF domain is linked to an adenylyl cyclase domain. The PAC protein mediates a photophobic response. In the AppA protein of Rhodobacter sphaeroides, the BLUF domain is linked to a downstream domain without similarity to known proteins. AppA functions as a transcriptional antirepressor, controlling photosynthesis gene expression in the purple bacterium R. sphaeroides in response to light and oxygen. We fused the PAC␣1-BLUF domain from Euglena to the C terminus of AppA. Our results show that the hybrid protein is fully functional in light-dependent gene repression in R. sphaeroides, despite only Ϸ30% identity between the eukaryotic and the bacterial BLUF domains. Furthermore, the bacterial BLUF domain and the C terminus of AppA can transmit the light signal even when expressed as separated domains. This finding implies that the BLUF domain is fully modular and can relay signals to completely different output domains.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.