The anticancer potential of the CLK kinases inhibitors 1C8 and GPS167 revealed by their impact on the epithelial-mesenchymal transition and the antiviral immune response.

The diheteroarylamide-based compound 1C8 and the aminothiazole carboxamide-related compound GPS167 inhibit the CLK kinases, and affect the proliferation of a broad range of cancer cell lines. A chemogenomic screen previously performed with GPS167 revealed that the depletion of components associated with mitotic spindle assembly altered sensitivity to GPS167. Here, a similar screen performed with 1C8 also established the impact of components involved in mitotic spindle assembly. Accordingly, transcriptome analyses of cells treated with 1C8 and GPS167 indicated that the expression and RNA splicing of transcripts encoding mitotic spindle assembly components were affected. The functional relevance of the microtubule connection was confirmed by showing that subtoxic concentrations of drugs affecting mitotic spindle assembly increased sensitivity to GPS167. 1C8 and GPS167 impacted the expression and splicing of transcripts in pathways relevant to tumor progression, including MYC targets and the epithelial mesenchymal transition (EMT). Finally, 1C8 and GPS167 altered the expression and alternative splicing of transcripts involved in the antiviral immune response. Consistent with this observation, depleting the double-stranded RNA sensor DHX33 suppressed GPS167-mediated cytotoxicity on HCT116 cells. Our study uncovered molecular mechanisms through which 1C8 and GPS167 affect cancer cell proliferation as well as processes critical for metastasis.

SRSF10: an atypical splicing regulator with critical roles in stress response, organ development, and viral replication.

Serine/arginine splicing factor 10 (SRSF10) is a member of the family of mammalian splicing regulators known as SR proteins. Like several of its SR siblings, the SRSF10 protein is composed of an RNA binding domain (RRM) and of arginine and serine-rich auxiliary domains (RS) that guide interactions with other proteins. The phosphorylation status of SRSF10 is of paramount importance for its activity and is subjected to changes during mitosis, heat-shock, and DNA damage. SRSF10 overexpression has functional consequences in a growing list of cancers. By controlling the alternative splicing of specific transcripts, SRSF10 has also been implicated in glucose, fat, and cholesterol metabolism, in the development of the embryonic heart, and in neurological processes. SRSF10 is also important for the proper expression and processing of HIV-1 and other viral transcripts. We discuss how SRSF10 could become a potentially appealing therapeutic target to combat cancer and viral infections.

A novel class of inhibitors that target SRSF10 and promote p53-mediated cytotoxicity on human colorectal cancer cells.

The elevated expression of the splicing regulator SRSF10 in metastatic colorectal cancer (CRC) stimulates the production of the pro-tumorigenic BCLAF1-L splice variant. We discovered a group of small molecules with an aminothiazole carboxamide core (GPS167, GPS192 and others) that decrease production of BCLAF1-L. While additional alternative splicing events regulated by SRSF10 are affected by GPS167/192 in HCT116 cells (e.g. in MDM4, WTAP, SLK1 and CLK1), other events are shifted in a SRSF10-independent manner (e.g. in MDM2, NAB2 and TRA2A). GPS167/192 increased the interaction of SRSF10 with the CLK1 and CLK4 kinases, leading us to show that GPS167/192 can inhibit CLK kinases preferentially impacting the activity of SRSF10. Notably, GPS167 impairs the growth of CRC cell lines and organoids, inhibits anchorage-independent colony formation, cell migration, and promotes cytoxicity in a manner that requires SRSF10 and p53. In contrast, GPS167 only minimally affects normal colonocytes and normal colorectal organoids. Thus, GPS167 reprograms the tumorigenic activity of SRSF10 in CRC cells to elicit p53-dependent apoptosis.

Cat and Mouse: HIV Transcription in Latency, Immune Evasion and Cure/Remission Strategies.

There is broad scientific and societal consensus that finding a cure for HIV infection must be pursued. The major barrier to achieving a cure for HIV/AIDS is the capacity of the HIV virus to avoid both immune surveillance and current antiretroviral therapy (ART) by rapidly establishing latently infected cell populations, termed latent reservoirs. Here, we provide an overview of the rapidly evolving field of HIV cure/remission research, highlighting recent progress and ongoing challenges in the understanding of HIV reservoirs, the role of HIV transcription in latency and immune evasion. We review the major approaches towards a cure that are currently being explored and further argue that small molecules that inhibit HIV transcription, and therefore uncouple HIV gene expression from signals sent by the host immune response, might be a particularly promising approach to attain a cure or remission. We emphasize that a better understanding of the game of "cat and mouse" between the host immune system and the HIV virus is a crucial knowledge gap to be filled in both cure and vaccine research.

BIM and NOXA are mitochondrial effectors of TAF6δ-driven apoptosis.

TAF6δ is a pro-apoptotic splice variant of the RNA polymerase II general transcription factor, TAF6, that can dictate life vs. death decisions in animal cells. TAF6δ stands out from classical pro-apoptotic proteins because it is encoded by a gene that is essential at the cellular level, and because it functions as a component of the basal transcription machinery. TAF6δ has been shown to modulate the transcriptome landscape, but it is not known if changes in gene expression trigger apoptosis nor which TAF6δ-regulated genes contribute to cell death. Here we used microarrays to interrogate the genome-wide impact of TAF6δ on transcriptome dynamics at temporal resolution. The results revealed changes in pro-apoptotic BH3-only mitochondrial genes that correlate tightly with the onset of cell death. These results prompted us to test and validate a role for the mitochondrial pathway by showing that TAF6δ expression causes cytochrome c release into the cytoplasm. To further dissect the mechanism by which TAF6δ drives apoptosis, we pinpointed BIM and NOXA as candidate effectors. siRNA experiments showed that both BIM and NOXA contribute to TAF6δ-dependent cell death. Our results identify mitochondrial effectors of TAF6δ-driven apoptosis, thereby providing the first of mechanistic framework underlying the atypical TAF6δ apoptotic pathway's capacity to intersect with the classically defined apoptotic machinery to trigger cell death.

Alternative splicing of TAF6: downstream transcriptome impacts and upstream RNA splice control elements.

The TAF6δ pathway of apoptosis can dictate life versus death decisions independently of the status of p53 tumor suppressor. TAF6δ is an inducible pro-apoptotic subunit of the general RNA polymerase II (Pol II) transcription factor TFIID. Alternative splice site choice of TAF6δ has been shown to be a pivotal event in triggering death via the TAF6δ pathway, yet nothing is currently known about the mechanisms that promote TAF6δ splicing. Furthermore the transcriptome impact of the gain of function of TAF6δ versus the loss of function of the major TAF6α splice form remains undefined. Here we employ comparative microarray analysis to show that TAF6δ drives a transcriptome profile distinct from that resulting from depletion of TAF6α. To define the cis-acting RNA elements responsible for TAF6δ alternative splicing we performed a mutational analysis of a TAF6 minigene system. The data point to several new RNA elements that can modulate TAF6δ and also reveal a role for RNA secondary structure in the selection of TAF6δ.