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KLF6-dependent transcription in renal cancer cells

ABSTRACT: The PDGF and mTOR pathways are clinically relevant therapeutic targets in clear cell renal cell carcinoma (ccRCC), but the molecular mechanisms that lead to their activation has remained poorly understood. By chromatin and transcriptomic profiling and functional analysis we have identified Kruppel like factor 6 (KLF6), a transcription factor of the zinc-finger family, as a critical regulator of the PDGF-mTOR axis in ccRCC. KLF6 expression is supported by one of the strongest super enhancers in ccRCC cells. Inhibition of KLF6 in several ccRCC cell lines impaired cell proliferation in vitro and in vivo and reduced metastatic lung colonization. KLF6 depletion led to downregulation of lipid homeostasis pathways downstream of SREBF1 and SREBF2, suggesting a role for KLF6 as a regulator of mTOR. We find that KLF6 modulates mTORC1 activity in ccRCC via transcriptionally regulating the expression of PDGFB, an activator of the PIK3-AKT-mTOR signalling pathway. Targeting PDGFB in ccRCC inhibited mTORC1, and supplementing KLF6-depleted cells with recombinant PDGFB rescued mTORC1 activity. Our data suggest that a robust super enhancer that integrates signals from multiple pathways, including the ccRCC-initiating VHL-HIF2A pathway, supports an autocrine PDGFB-dependent signalling loop that promotes mTOR activity in ccRCC. These results suggest the possibility that combining low dose PDGFR and mTOR inhibition could be a viable therapeutic strategy for ccRCC.

ORGANISM(S): Homo sapiens

PROVIDER: GSE115763 | GEO | 2019/03/20

REPOSITORIES: GEO

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Project description:The mechanistic target of rapamycin (mTOR) pathway integrates diverse environmental inputs, including immune signals and metabolic cues, to direct T cell fate decisions1. Activation of mTOR, comprised of mTORC1 and mTORC2 complexes, delivers an obligatory signal for proper activation and differentiation of effector CD4+ T cells2,3, whereas in the regulatory T cell (Treg) compartment, the Akt-mTOR axis is widely acknowledged as a crucial negative regulator of Treg de novo differentiation4-8 and population expansion9. However, whether mTOR signaling affects the homeostasis and function of Tregs remains largely unexplored. Here we show that mTORC1 signaling is a pivotal positive determinant of Treg function. Tregs have elevated steady-state mTORC1 activity compared to naïve T cells. Signals via T cell receptor (TCR) and IL-2 provide major inputs for mTORC1 activation, which in turn programs suppressive function of Tregs. Disruption of mTORC1 through Treg-specific deletion of the essential component Raptor leads to a profound loss of Treg suppressive activity in vivo and development of a fatal early-onset inflammatory disorder. Mechanistically, Raptor/mTORC1 signaling in Tregs promotes cholesterol/lipid metabolism, with the mevalonate pathway particularly important for coordinating Treg proliferation and upregulation of suppressive molecules CTLA-4 and ICOS to establish Treg functional competency. In contrast, mTORC1 does not directly impact the expression of Foxp3 or anti- and pro-inflammatory cytokines in Tregs, suggesting a non-conventional mechanism for Treg functional regulation. Lastly, we provide evidence that mTORC1 maintains Treg function partly through inhibiting the mTORC2 pathway. Our results demonstrate that mTORC1 acts as a fundamental ‘rheostat’ in Tregs to link immunological signals from TCR and IL-2 to lipogenic pathways and functional fitness, and highlight a central role of metabolic programming of Treg suppressive activity in immune homeostasis and tolerance. We used microarrays to explore the gene expression profiles differentially expressed in regulatory T-cells from wild-type and CD4(cre) x Raptor(fl/fl) mice

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KLF6-dependent transcription in renal cancer cells

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