Specific Binding Partners Research Articles

Pervasive functional translation of noncanonical human open reading frames.

Ribosome profiling has revealed pervasive but largely uncharacterized translation outside of canonical coding sequences (CDSs). In this work, we exploit a systematic CRISPR-based screening strategy to identify hundreds of noncanonical CDSs that are essential for cellular growth and whose disruption elicits specific, robust transcriptomic and phenotypic changes in human cells. Functional characterization of the encoded microproteins reveals distinct cellular localizations, specific protein binding partners, and hundreds of microproteins that are presented by the human leukocyte antigen system. We find multiple microproteins encoded in upstream open reading frames, which form stable complexes with the main, canonical protein encoded on the same messenger RNA, thereby revealing the use of functional bicistronic operons in mammals. Together, our results point to a family of functional human microproteins that play critical and diverse cellular roles.

Selective targeting of TET catalytic domain promotes somatic cell reprogramming

Ten-eleven translocation (TET) family enzymes (TET1, TET2, and TET3) oxidize 5-methylcytosine (5mC) and generate 5-hydroxymethylcytosine (5hmC) marks on the genome. Each TET protein also interacts with specific binding partners and partly plays their role independent of catalytic activity. Although the basic role of TET enzymes is well established now, the molecular mechanism and specific contribution of their catalytic and noncatalytic domains remain elusive. Here, by combining in silico and biochemical screening strategy, we have identified a small molecule compound, C35, as a first-in-class TET inhibitor that specifically blocks their catalytic activities. Using this inhibitor, we explored the enzymatic function of TET proteins during somatic cell reprogramming. Interestingly, we found that C35-mediated TET inactivation increased the efficiency of somatic cell programming without affecting TET complexes. Using high-throughput mRNA sequencing, we found that by targeting 5hmC repressive marks in the promoter regions, C35-mediated TET inhibition activates the transcription of the BMP-SMAD-ID signaling pathway, which may be responsible for promoting somatic cell reprogramming. These results suggest that C35 is an important tool for inducing somatic cell reprogramming, as well as for dissecting the other biological functions of TET enzymatic activities without affecting their other nonenzymatic roles.

Ubiquitin-specific protease 8 (USP8/UBPy): a prototypic multidomain deubiquitinating enzyme with pleiotropic functions.

Protein modification by ubiquitin is one of the most versatile posttranslational regulations and counteracted by almost 100 deubiquitinating enzymes (DUBs). USP8 was originally identified as a growth regulated ubiquitin-specific protease and is like many other DUBs characterized by its multidomain architecture. Besides the catalytic domain, specific protein–protein interaction modules were characterized which contribute to USP8 substrate recruitment, regulation and targeting to distinct protein complexes. Studies in mice and humans impressively showed the physiological relevance and non-redundant function of USP8 within the context of the whole organism. USP8 knockout (KO) mice exhibit early embryonic lethality while induced deletion in adult animals rapidly causes lethal liver failure. Furthermore, T-cell specific ablation disturbs T-cell development and function resulting in fatal autoimmune inflammatory bowel disease. In human patients, somatic mutations in USP8 were identified as the underlying cause of adrenocorticotropic hormone (ACTH) releasing pituitary adenomas causing Cushing's disease (CD). Here we provide an overview of the versatile molecular, cellular and pathology associated function and regulation of USP8 which appears to depend on specific protein binding partners, substrates and the cellular context.

Upregulation of PUM1 Expression in Preeclampsia Impairs Trophoblast Invasion by Negatively Regulating the Expression of the lncRNA HOTAIR.

Pumilio (PUM) proteins are members of a highly conserved RNA-binding protein family that posttranscriptionally regulate gene expression in many organisms. However, their roles in the placenta are unclear. In the present study, we report the requirement for the PUM homolog 1 (PUM1) gene in preeclampsia (PE). Immunofluorescence and immunohistochemical data showed that PUM1 was highly expressed in human placental villi from women with PE compared to healthy controls (HCs). Further, PUM1 overexpression repressed, and knockdown enhanced, the invasion and proliferation of trophoblasts. Interestingly, PUM1 knockdown promoted trophoblast invasion in a villous explant culture model, while PUM1 overexpression repressed these effects. Furthermore, lncRNA transcriptome sequencing coupled with RNA immunoprecipitation (RIP) revealed that PUM1 inhibits trophoblast invasion in PE by downregulating the expression of lncRNA HOTAIR. Moreover, PUM1 regulates HOTAIR expression via a posttranscriptional mechanism. Using RNA-protein pull-down and mRNA stability assays, we identified PUM1 as a specific binding partner that decreased the half-life of HOTAIR and lowered the steady-state level of HOTAIR expression, suggesting a novel posttranscriptional regulatory mechanism. Collectively, these findings identified a novel RNA regulatory mechanism, revealing a new pathway governing the regulation of PUM1/HOTAIR in trophoblast invasion in the pathogenesis of PE.

NIMA-related kinase 7 interacts with Mat1 and is involved in the UV-induced DNA Damage Response

Nek7 is a serine/threonine kinase of the mammalian NIMA-related kinases (Neks) family, which members are involved in the regulation of the progression of the cell cycle. Although several Nek members have been associated with a range of cell cycle-related tasks, including DNA repair, a possible role of Nek7 in the DNA-damage response is so far unknown. Here, we employed in vitro and in vivo interaction assays to identify Mat1 as a specific Nek7 binding partner and substrate. In addition, we showed that Nek7 pulled down both CDK7 and cyclin H and directly phosphorylated Mat1, indicating that Nek7 may play a role in the regulation of the CAK complex. Furthermore, we showed that both Nek7 and Mat1 depletion led to an accumulation of cells in the S-phase, decreased cell proliferation and increased apoptosis . Notably, the mutational ablation of kinase Nek7 activity also induced increased apoptosis upon DNA damage. Collectively, our findings support the notion that Nek7 may cooperate with Mat1 in signal pathways that govern the cell cycle machinery including DDR, S-phase progression and apoptosis, and thereby can constitute an important novel player for in the context of cellular transformation and tumorigenesis.

Surface expression of TTYH2 is attenuated by direct interaction with β-COP

TTYH2 is a calcium-activated, inwardly rectifying anion channel that has been shown to be related to renal cancer and colon cancer. Based on the topological prediction, TTYH2 protein has five transmembrane domains with the extracellular N-terminus and the cytoplasmic C-terminus. In the present study, we identified a vesicle transport protein, β-COP, as a novel specific binding partner of TTYH2 by yeast two-hybrid screening using a human brain cDNA library with the C-terminal region of TTYH2 (TTYH2-C) as a bait. Using in vitro and in vivo binding assays, we confirmed the protein-protein interactions between TTYH2 and β-COP. We also found that the surface expression and activity of TTYH2 were decreased by co-expression with β-COP in the heterologous expression system. In addition, β-COP associated with TTYH2 in a native condition at a human colon cancer cell line, LoVo cells. The over-expression of β-COP in the LoVo cells led to a dramatic decrease in the surface expression and activity of endogenous TTYH2. Collectively, these data suggested that β-COP plays a critical role in the trafficking of the TTYH2 channel to the plasma membrane.

Abstract 4587: The N-terminal domain of HARS is a novel NRP2 ligand and can regulate NRP2-dependent macrophage function

Abstract Tumor-associated macrophages (TAM) are associated with regulation of antitumor immune responses, and neuropilin-2 (NRP2), a pleiotropic receptor with an emerging role in immune responses, has recently been demonstrated to be important for this activity (Roy et al, Cancer Res. 2018). Deletion of NRP2 results in impaired clearance of apoptotic tumor cells through reduced efferocytosis, which plays a role in tumor promotion. We now show that the N-terminal domain of the histidyl-tRNA synthetase (HARS) is a specific binding partner of NRP2, and can regulate the phagocytic function of NRP2 in macrophages. The HARS N-terminal domain, which is found only in higher eukaryotes, is conserved among splice variants of HARS and has evolved to regulate immune cell engagement. Incubation of macrophages with recombinant HARS N-terminal domain, had no effect on phagocytic uptake, but significantly impaired the maturation of phagosomes in a dose dependent manner. This phenotype mimics that of the NRP2 knockout, suggesting pharmacological intervention with this agent to modulate NRP2 driven biology may be possible. Citation Format: Navatha Shree Sharma, Samikshan Dutta, Steve Crampton, Sanna Rosengren, Kaustubh Datta. The N-terminal domain of HARS is a novel NRP2 ligand and can regulate NRP2-dependent macrophage function [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4587.

Human LC3 and GABARAP subfamily members achieve functional specificity via specific structural modulations

ABSTRACTAutophagy is a conserved adaptive cellular pathway essential to maintain a variety of physiological functions. Core components of this machinery are the six human Atg8 orthologs that initiate formation of appropriate protein complexes. While these proteins are routinely used as indicators of autophagic flux, it is presently not possible to discern their individual biological functions due to our inability to predict specific binding partners. In our attempts towards determining downstream effector functions, we developed a computational pipeline to define structural determinants of human Atg8 family members that dictate functional diversity. We found a clear evolutionary separation between human LC3 and GABARAP subfamilies and also defined a novel sequence motif responsible for their specificity. By analyzing known protein structures, we observed that functional modules or microclusters reveal a pattern of intramolecular network, including distinct hydrogen bonding of key residues (F52/Y49; a subset of HP2) that may directly modulate their interaction preferences. Multiple molecular dynamics simulations were performed to characterize how these proteins interact with a common protein binding partner, PLEKHM1. Our analysis showed remarkable differences in binding modes via intrinsic protein dynamics, with PLEKHM1-bound GABARAP complexes showing less fluctuations and higher number of contacts. We further mapped 373 genomic variations and demonstrated that distinct cancer-related mutations are likely to lead to significant structural changes. Our findings present a quantitative framework to establish factors underlying exquisite specificity of human Atg8 proteins, and thus facilitate the design of precise modulators.Abbreviations: Atg: autophagy-related; ECs: evolutionary constraints; GABARAP: GABA type A receptor-associated protein; HsAtg8: human Atg8; HP: hydrophobic pocket; KBTBD6: kelch repeat and BTB domain containing 6; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MD: molecular dynamics; HIV-1 Nef: human immunodeficiency virus type 1 negative regulatory factor; PLEKHM1: pleckstrin homology and RUN domain containing M1; RMSD: root mean square deviation; SQSTM1/p62: sequestosome 1; WDFY3/ALFY: WD repeat and FYVE domain containing 3

Fluorogenic Photoaffinity Labeling of Proteins in Living Cells.

Genetically encoded fluorescent proteins or small-molecule probes that recognize specific protein binding partners can be used to label proteins to study their localization and function with fluorescence microscopy. However, these approaches are limited in signal-to-background resolution and the ability to temporally control labeling. Herein, we describe a covalent protein labeling technique using a fluorogenic malachite green probe functionalized with a photoreactive cross-linker. This enables a controlled covalent attachment to a genetically encodable fluorogen activating protein (FAP) with low background signal. We demonstrate covalent labeling of a protein in vitro as well as in live mammalian cells. This method is straightforward, displays high labeling specificity, and results in improved signal-to-background ratios in photoaffinity labeling of target proteins. Additionally, this probe provides temporal control over reactivity, enabling future applications in real-time monitoring of cellular events.

Relative interfacial cleavage energetics of protein complexes revealed by surface collisions

To fulfill their biological functions, proteins must interact with their specific binding partners and often function as large assemblies composed of multiple proteins or proteins plus other biomolecules. Structural characterization of these complexes, including identification of all binding partners, their relative binding affinities, and complex topology, is integral for understanding function. Understanding how proteins assemble and how subunits in a complex interact is a cornerstone of structural biology. Here we report a native mass spectrometry (MS)-based method to characterize subunit interactions in globular protein complexes. We demonstrate that dissociation of protein complexes by surface collisions, at the lower end of the typical surface-induced dissociation (SID) collision energy range, consistently cleaves the weakest protein:protein interfaces, producing products that are reflective of the known structure. We present here combined results for multiple complexes as a training set, two validation cases, and four computational models. We show that SID appearance energies can be predicted from structures via a computationally derived expression containing three terms (number of residues in a given interface, unsatisfied hydrogen bonds, and a rigidity factor).

Investigating the Mechanisms by which the Methyl‐CpG Binding Protein ZBTB38 Identifies Interacting Partners and Mediates Transcription

Cytosine methylation in CpG dinucleotides is an essential epigenetic modification utilized for regulating transcriptional processes within the eukaryotic genome. Consequently, misappropriation of DNA methylation patterns is associated with many diseases, including cancer. At many gene promoters, DNA methylation mediates expression through recruitment of methyl‐CpG binding proteins (MBPs). These specialized transcription factors read the methylated DNA signal and subsequently recruit chromatin remodeling complexes; leading to alterations in chromatin architecture and transcriptional responses. Thus, MBPs represent important functional intermediaries between these two key epigenetic events. ZBTB38 is the largest member of the ZBTB family of MBPs and contains two sets of five Cys2His2 zinc finger (ZF) domains distributed into N‐ and C‐terminal clusters, as well as an N‐terminal BTB/POZ protein interaction domain. There is increasing evidence that ZBTB38 regulates transcription for several core cellular processes in both normal cells as well as disease states. However, full mechanistic insight for how ZBTB38 identifies binding partners to elicit cellular function remains to be determined. Using combined structural and biochemical approaches, specific DNA binding partners have been identified and characterized for both the N‐ and C‐terminal ZF domains of ZBTB38. Importantly, we recently discovered that in addition to the N‐terminal ZFs, the C‐terminal ZFs also exhibit methyl‐selective DNA binding through the use of an alternative mode for methylated DNA recognition. Cell based studies have been utilized to begin delineating how these two ZF domains may function together or independently to modulate transcription. In addition to DNA interactions, we have begun to evaluate protein interacting partners for ZBTB38 using a combination of biophysical and cell based methodologies. Together, these findings expand our understanding for ZF recognition of methylated DNA, as well as illuminate the molecular basis by which ZBTB38 preferentially recognizes its biomolecular binding partners to translate transcriptional outcomes into specific cellular responses.Support or Funding InformationThis work was supported in part by MCB‐1715370 from the National Science Foundation and by RSG‐14‐185‐01‐DMC from the American Cancer Society.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Deciphering the galectin-12 protein interactome reveals a major impact of galectin-12 on glutamine anaplerosis in colon cancer cells

Galectins are β-galactoside binding proteins which possess a variety of functions including modulation of apoptosis, growth and differentiation. Hence, alterations in the expression profile have been associated with loss of cellular homeostasis contributing to tumor growth and progression. Though galectin-12 is significantly downregulated in several tumor entities, including colon cancer, its impact on cellular homeostasis as well as galectin-12 specific binding partners have not been identified so far. We therefore established an experimental strategy which is based on reversible cross-link immunoprecipitation to capture the galectin-12 protein interactome in colon cancer cells. By applying this approach, we identified 10 novel candidates of galectin-12 interacting proteins including the neutral amino acid exchanger SLC1A5. Remarkably, we uncovered that binding of galectin-12 to SLC1A5 significantly reduced glutamine uptake in our model cell line. Consequently, utilization of glutamine carbon for biomass synthesis was profoundly affected, suggesting galectin-12 as a novel inhibitor of glutamine anaplerosis in colon cancer cells. More detailed analysis revealed that colon cancer cells can counteract galectin-12 mediated glutamine deprivation by induction of compensatory mechanisms which facilitate adaption to low-glutamine conditions and thus survival.

Regulation of cell migration by α4 and α9 integrins.

Integrins are heterodimeric transmembrane receptors that play an essential role in enabling cells to sense and bind to extracellular ligands. Activation and clustering of integrins leads to the formation of focal adhesions at the plasma membrane that subsequently initiate signalling pathways to control a broad range of functional endpoints including cell migration, proliferation and survival. The α4 and α9 integrins form a small sub-family of receptors that share some specific ligands and binding partners. Although relatively poorly studied compared with other integrin family members, emerging evidence suggests that despite restricted cell and tissue expression profiles, these integrins play a key role in the regulation of signalling pathways controlling cytoskeletal remodelling and migration in both adherent and non-adherent cell types. This review summarises the known shared and specific roles for α4 and α9 integrins and highlights the importance of these receptors in controlling cell migration within both homeostatic and disease settings.

Structural and Dynamical Order of a Disordered Protein: Molecular Insights into Conformational Switching of PAGE4 at the Systems Level.

Folded proteins show a high degree of structural order and undergo (fairly constrained) collective motions related to their functions. On the other hand, intrinsically disordered proteins (IDPs), while lacking a well-defined three-dimensional structure, do exhibit some structural and dynamical ordering, but are less constrained in their motions than folded proteins. The larger structural plasticity of IDPs emphasizes the importance of entropically driven motions. Many IDPs undergo function-related disorder-to-order transitions driven by their interaction with specific binding partners. As experimental techniques become more sensitive and become better integrated with computational simulations, we are beginning to see how the modest structural ordering and large amplitude collective motions of IDPs endow them with an ability to mediate multiple interactions with different partners in the cell. To illustrate these points, here, we use Prostate-associated gene 4 (PAGE4), an IDP implicated in prostate cancer (PCa) as an example. We first review our previous efforts using molecular dynamics simulations based on atomistic AWSEM to study the conformational dynamics of PAGE4 and how its motions change in its different physiologically relevant phosphorylated forms. Our simulations quantitatively reproduced experimental observations and revealed how structural and dynamical ordering are encoded in the sequence of PAGE4 and can be modulated by different extents of phosphorylation by the kinases HIPK1 and CLK2. This ordering is reflected in changing populations of certain secondary structural elements as well as in the regularity of its collective motions. These ordered features are directly correlated with the functional interactions of WT-PAGE4, HIPK1-PAGE4 and CLK2-PAGE4 with the AP-1 signaling axis. These interactions give rise to repeated transitions between (high HIPK1-PAGE4, low CLK2-PAGE4) and (low HIPK1-PAGE4, high CLK2-PAGE4) cell phenotypes, which possess differing sensitivities to the standard PCa therapies, such as androgen deprivation therapy (ADT). We argue that, although the structural plasticity of an IDP is important in promoting promiscuous interactions, the modulation of the structural ordering is important for sculpting its interactions so as to rewire with agility biomolecular interaction networks with significant functional consequences.

A First Step toward Understanding Obscurin's Molecular Mechanism

Obscurin is a giant (800-950 kDa) cytoskeletal protein involved in mobility and adhesion signaling pathways. It is the second most mutated gene in breast and colorectal cancers, and in muscles mutated obscurin leads to muscular dystrophy and cardiomyopathy. Obscurin's specific role in these diseases remains an active area of research. In an effort to better understand obscurin's molecular mechanism of action, here we describe an experimental approach to elucidate obscurin binding partners in eukaryotic cells. We have designed a series of constructs containing a promiscuous biotin ligase, and transfected this DNA into MDCK II epithelial cells. The resulting microscopy images and SDS-PAGE gels give us our first understanding of obscurin subcellular localization in non-muscle cells, and provide a proof-of-concept platform to conduct future BioID assays on similar samples to identify specific binding partners.

LHX1-a multifunctional regulator in preoptic area-derived interneuron development.

LHX1-a multifunctional regulator in preoptic area-derived interneuron development.

CACYBP Enhances Cytoplasmic Retention of P27Kip1 to Promote Hepatocellular Carcinoma Progression in the Absence of RNF41 Mediated Degradation.

Calcyclin-binding protein (CACYBP) is a multi-ligand protein implicated in the progression of various human cancers. However, its function in hepatocellular carcinoma (HCC) remains unknown.Methods: The expression of CACYBP and RNF41 (RING finger protein 41) in HCC cancer and adjacent non-tumor tissues was detected by immunohistochemistry. CCK-8 assays, colony formation assays, flow cytometry detection and xenograft models were used to evaluate the impact of CACYBP expression on HCC cell growth, apoptosis and cell cycle regulation. Immunoprecipitation and ubiquitination assays were performed to determine how RNF41 regulates CACYBP. The regulatory mechanism of RNF41-CACYBP signaling axis on P27Kip1 was investigated by western blotting and immunofluorescence.Results: CACYBP was highly expressed and associated with poor prognosis in HCC. CACYBP expression was required for HCC cell growth in vitro and in vivo. Moreover, we identified RNF41 as a specific binding partner of CACYBP at exogenous and endogenous levels. RNF41 recruited CACYBP by its C-terminal substrate binding domain, subsequently ubiquitinating CACYBP and promoting its degradation in both proteasome- and lysosome-dependent pathways. In HCC tissues, RNF41 expression was reduced and conferred a negative correlation with CACYBP expression. Mechanistically, CACYBP overexpression stimulated the Ser10, Thr157 and Thr198 phosphorylation of P27Kip1 and its cytoplasmic retention, and RNF41 co-expression attenuated this phenomenon. CACYBP depletion led to decreased levels of cyclin D1, cyclin A2, CDK2 and CDK4, causing a typical cell cycle arrest at G1/S phase and increasing apoptosis in HCC cells. P27Kip1-S10D but not P27Kip1-S10A reconstitution rescued partially the cell cycle function and apoptotic feature after CACYBP depletion.Conclusion: Our findings provide novel insights into the functional role and regulatory mechanism of CACYBP in HCC.

Signal Transduction Via Co-stimulatory and Co-inhibitory Receptors.

T-cell receptor (TCR)-mediated antigen-specific stimulation is essential for initiating T-cell activation. However, signaling through the TCR alone is not sufficient for inducing an effective response. In addition to TCR-mediated signaling, signaling through antigen-independent co-stimulatory or co-inhibitory receptors is critically important not only for the full activation and functional differentiation of T cells but also for the termination and suppression of T-cell responses. Many studies have investigated the signaling pathways underlying the function of each molecular component. Co-stimulatory and co-inhibitory receptors have no kinase activity, but their cytoplasmic region contains unique functional motifs and potential phosphorylation sites. Engagement of co-stimulatory receptors leads to recruitment of specific binding partners, such as adaptor molecules, kinases, and phosphatases, via recognition of a specific motif. Consequently, each co-stimulatory receptor transduces a unique pattern of signaling pathways. This review focuses on our current understanding of the intracellular signaling pathways provided by co-stimulatory and co-inhibitory molecules, including B7:CD28 family members, immunoglobulin, and members of the tumor necrosis factor receptor superfamily.

Inhibition of heat shock protein 70 blocks the development of cardiac hypertrophy by modulating the phosphorylation of histone deacetylase 2.

Previously, we reported that phosphorylation of histone deacetylase 2 (HDAC2) and the resulting activation causes cardiac hypertrophy. Through further study of the specific binding partners of phosphorylated HDAC2 and their mechanism of regulation, we can better understand how cardiac hypertrophy develops. Thus, in the present study, we aimed to elucidate the function of one such binding partner, heat shock protein 70 (HSP70). Primary cultures of rat neonatal ventricular cardiomyocytes and H9c2 cardiomyoblasts were used for in vitro cellular experiments. HSP70 knockout (KO) mice and transgenic (Tg) mice that overexpress HSP70 in the heart were used for in vivo analysis. Peptide-precipitation and immunoprecipitation assay revealed that HSP70 preferentially binds to phosphorylated HDAC2 S394. Forced expression of HSP70 increased phosphorylation of HDAC2 S394 and its activation, but not that of S422/424, whereas knocking down of HSP70 reduced it. However, HSP70 failed to phosphorylate HDAC2 in the cell-free condition. Phosphorylation of HDAC2 S394 by casein kinase 2α1 enhanced the binding of HSP70 to HDAC2, whereas dephosphorylation induced by the catalytic subunit of protein phosphatase 2A (PP2CA) had the opposite effect. HSP70 prevented HDAC2 dephosphorylation by reducing the binding of HDAC2 to PP2CA. HSP70 KO mouse hearts failed to phosphorylate S394 HDAC2 in response to isoproterenol infusion, whereas Tg overexpression of HSP70 increased the phosphorylation and activation of HDAC2. 2-Phenylethynesulfonamide (PES), an HSP70 inhibitor, attenuated cardiac hypertrophy induced either by phenylephrine in neonatal ventricular cardiomyocytes or by aortic banding in mice. PES reduced HDAC2 S394 phosphorylation and its activation by interfering with the binding of HSP70 to HDAC2. These results demonstrate that HSP70 specifically binds to S394-phosphorylated HDAC2 and maintains its phosphorylation status, which results in HDAC2 activation and the development of cardiac hypertrophy. Inhibition of HSP70 has possible application as a therapeutic.

KLHL5 knockdown increases cellular sensitivity to anticancer drugs.

KLHL family genes are noted for their involvement in the E3 ligase ubiquitination pathway through binding with Cullin-3 (CUL3) resulting in degradation of specific binding partners. KLHLs are thus intriguing genes for cancer as they can directly influence the degradation of therapeutically relevant cell cycle regulators such as Aurora Kinase, PLK1, or CDK1. However, most KLHL family members remain understudied within the literature. This study explores the relationship of expression of KLHL member, KLHL5, with the pharmacologic effect of anti-cancer drugs. KLHL5 knockdown decreased the proliferation and viability of cancer cells and sensitized cancer cells to numerous anti-cancer drugs. Drugs related to cell cycle including Akt/PI3K/mTOR inhibitors were especially sensitized by KLHL5 knockdown. The potential of KLHL5 as a prognostic or diagnostic cancer marker was compared to other KLHLs through a pan-cancer study of The Cancer Genome Atlas (TCGA) tumor groups. While KLHL5 expression shows marginal dysregulation in cancer, other KLHLs exhibit significant dysregulation in all cancer types, and exceptionally in renal carcinomas. This study advocates for further study of KLHLs as potential alternative therapeutic targets, since while KLHL5 is a novel gene impacting anticancer drug effects, others may have a similar impact on drug effect while having greater potential as diagnostic or prognostic markers.