Transcription factors comprise just over 7% of the human proteome and serve as the gatekeepers of cellular function, integrating external signal information into gene expression programs that reconfigure cellular physiology at the most basic levels. Surface-initiated, cell signaling pathways converge on transcription factors, decorating these proteins with an array of post-translational modifications (PTMs) that are often interdependent, being linked in time, space, and combinatorial function. These PTMs orchestrate every activity of a transcription factor over its entire lifespan—from subcellular localization to protein–protein interactions, sequence-specific DNA binding, transcriptional regulatory activity, and protein stability—and play key roles in the epigenetic regulation of gene expression. The multitude of PTMs of transcription factors also offers numerous potential points of intervention for development of therapeutic agents to treat a wide spectrum of diseases. We review PTMs most commonly targeting transcription factors, focusing on recent reports of sequential and linked PTMs of individual factors.

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Chicken ovalbumin upstream promoter transcription factor (COUP-TF)-interacting protein 2 (CTIP2), also known as Bcl11b, is a transcriptional repressor that functions by direct, sequence-specific DNA binding activity or by recruitment to the promoter template by interaction with COUP-TF family members. CTIP2 is essential for both T cell development and axonal projections of corticospinal motor neurons in the central nervous system. However, little is known regarding the molecular mechanism(s) by which CTIP2 contributes to either process. CTIP2 complexes that were isolated from SK-N-MC neuroblastoma cells were found to harbor substantial histone deacetylase activity, which was likely conferred by the nucleosome remodeling and deacetylation (NuRD) complex. CTIP2 was found to associate with the NuRD complex through direct interaction with both RbAp46 and RbAp48, and components of the NuRD complex were found to be recruited to an artificial promoter template in a CTIP2-dependent manner in transfected cells. Finally, the NuRD complex and CTIP2 were found to co-occupy the promoter template of p57KIP2, a gene encoding a cyclin-dependent kinase inhibitor, and identified herein as a novel transcriptional target of CTIP2 in SK-N-MC cells. Therefore, it seems likely that the NuRD complex may be involved in transcriptional repression of CTIP2 target genes and contribute to the function(s) of CTIP2 within a neuronal context.

Activation of the heterotrimeric G protein Gq causes cardiomyocyte hypertrophy in vivo and in cell culture models. Hypertrophic responses induced by pressure or volume overload are exacerbated by increased Gq activity and ameliorated by Gq inhibition. Gq activates phospholipase Cbeta (PLCbeta) subtypes, resulting in generation of the intracellular messengers inositol(1,4,5)tris-phosphate [Ins(1,4,5)P(3)] and sn-1,2-diacylglycerol (DAG), which regulate intracellular Ca(2+) and conventional protein kinase C subtypes, respectively. Gq can also signal independently of PLCbeta, and the involvement of either Ins(1,4,5)P(3) or DAG in cardiomyocyte hypertrophy has not been unequivocally established. Overexpression of one splice variant of PLCbeta1, specifically PLCbeta1b, in neonatal rat cardiomyocytes causes increased cell size, elevated protein/DNA ratio, and heightened expression of the hypertrophy-related marker gene, atrial natriuretic peptide. The other splice variant, PLCbeta1a, had no effect. Expression of a 32-aa C-terminal PLCbeta1b peptide, which competes with PLCbeta1b for sarcolemmal association, prevented PLC activation and eliminated hypertrophic responses initiated by Gq or Gq-coupled alpha(1)-adrenergic receptors. In contrast, a PLCbeta1a C-terminal peptide altered neither PLC activity nor cellular hypertrophy. We conclude that hypertrophic responses initiated by Gq are mediated specifically by PLCbeta1b. Preventing PLCbeta1b association with the sarcolemma may provide a useful therapeutic target to limit hypertrophy.

Background:The transcription factor Bcl11b plays essential roles during T-cell development. Results: Bcl11b activity in thymocytes is regulated by MAPK-mediated phosphorylation and subsequent sumoylation and ubiquitination. Conclusion: A regulatory pathway links thymocyte stimulation, MAPK activation, and Bcl11b-dependent regulation of gene expression during late T-cell development. Significance: This work has implications for the role of Bcl11b in T-cell development and leukemogenesis.

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The signaling mediated by the chemokine receptor CXC chemokine receptor 2 (CXCR2) plays an important role in promoting the progression of many cancers, including pancreatic cancer, one of the most lethal human malignancies. CXCR2 possesses a consensus PSD-95/DlgA/ZO-1 (PDZ) motif at its carboxyl termini, which might interact with potential PDZ scaffold/adaptor proteins. We have previously reported that CXCR2 PDZ motif-mediated protein interaction is an important regulator for neutrophil functions. Here, using a series of biochemical assays, we demonstrate that CXCR2 is physically coupled to its downstream effector phospholipase C-β3 (PLC-β3) that is mediated by PDZ scaffold protein Na(+)/H(+) exchange regulatory factor 1 (NHERF1) into a macromolecular signaling complex both in vitro and in pancreatic cancer cells. We also observe that disrupting the CXCR2 complex, by gene delivery or peptide delivery of exogenous CXCR2 C-tail, significantly inhibits the biologic functions of pancreatic cancer cells (i.e., proliferation and invasion) in a PDZ motif-dependent manner. In addition, using a human pancreatic tumor xenograft model, we show that gene delivery of CXCR2 C-tail sequence (containing the PDZ motif) by adeno-associated virus type 2 viral vector potently suppresses human pancreatic tumor growth in immunodeficient mice. In summary, our results suggest the existence of a physical and functional coupling of CXCR2 and PLC-β3 mediated through NHERF1, forming a macromolecular complex that is critical for efficient and specific CXCR2 signaling in pancreatic cancer progression. Disrupting this CXCR2 complex could represent a novel and effective treatment strategy against pancreatic cancer.

Activation of the heterotrimeric G protein Gq causes cardiomyocyte hypertrophy in vivo and in cell models. Our previous studies have shown that responses to activated Gq in cardiomyocytes are mediated exclusively by phospholipase Cβ1b (PLCβ1b), because only this PLCβ subtype localizes at the cardiac sarcolemma. In the current study, we investigated the proteins involved in targeting PLCβ1b to the sarcolemma in neonatal rat cardiomyocytes. PLCβ1b, but not PLCβ1a, coimmunoprecipitated with the high-MW scaffolding protein SH3 and ankyrin repeat protein 3 (Shank3), as well as the known Shank3-interacting protein α-fodrin. The 32-aa splice-variant-specific C-terminal tail of PLCβ1b also associated with Shank3 and α-fodrin, indicating that PLCβ1b binds via the C-terminal sequence. Shank3 colocalized with PLCβ1b at the sarcolemma, and both proteins were enriched in the light membrane fractions. Knockdown of Shank3 using siRNA reduced PLC activation and downstream hypertrophic responses, demonstrating the importance of sarcolemmal localization for PLC signaling. These data indicate that PLCβ1b associates with a Shank3 complex at the cardiac sarcolemma via its splice-variant-specific C-terminal tail. Sarcolemmmal localization is central to PLC activation and subsequent downstream signaling following Gq-coupled receptor activation.