Project description:CDK4/6 kinase inhibitors have shown great promise in clinical trials in various cancer types and have recently entered clinical trial for advanced prostate cancer. Although patients are expected to respond well to this class of drugs, development of resistance in some patients is anticipated. To pre-empt this and study how prostate cancer may evade CDK4/6 inhibition, new resistance models were generated from LNCaP and LAPC4 prostate cancer cells cells by prolonged culturing in presence of 0.5uM palbociclib. A shotgun phosphoproteomics approach was utilized and integrated with RNA sequencing data to unravel the molecular underpinnings of acquired resistance to palbociclib and resultant broad CDK4/6 inhibitor resistance.
Project description:CDK4/6 kinase inhibitors have shown great promise in clinical trials in various cancer types and have recently entered clinical trial for advanced prostate cancer. Although patients are expected to respond well to this class of drugs, development of resistance in some patients is anticipated. To pre-empt this and study how prostate cancer may evade CDK4/6 inhibition, new resistance models were generated from LNCaP and LAPC4 prostate cancer cells cells by prolonged culturing in presence of 0.5uM palbociclib. RNA sequencing data was integrated with phospho-proteomics to unravel the molecular underpinnings of acquired resistance to palbociclib and resultant broad CDK4/6 inhibitor resistance.
Project description:The tumor suppressor protein RB acts as a transcription repressor via the interaction of its pocket domain with an L/IXCXE motif in HDAC proteins such as HDAC1. Here we demonstrated that while lacking an L/IXCXE motif, HDAC5 interacts with both RB-N (via an FXXXV motif) and RB-C segments and this interaction is diminished by RB serine-249/threonine-252 and threonine-821 phosphorylation. HDAC5 gene is frequently downregulated or deleted in human cancers such as prostate cancer. Loss of HDAC5 increases histone H3 lysine 27 acetylation (H3K27-ac) and circumvents RB-mediated repression of cell cycle-related oncogenic genes. Accordingly, HDAC5 loss confers resistance to the CDK4/6 inhibitors such as Palbociclib in prostate cancer cells in vitro and in mice, but this effect is overcome by the BET-CBP/p300 dual inhibitor NEO2734. Our findings reveal an unknown role of HDAC5 in RB-mediated histone deacetylation and gene repression and a mechanism modulating CDK4/6 inhibitor therapeutic sensitivity in cancer cells.
Project description:Kynureninase is a member of a large family of catalytically diverse but structurally homologous pyridoxal 5'-phosphate (PLP) dependent enzymes known as the aspartate aminotransferase superfamily or alpha-family. The Homo sapiens and other eukaryotic constitutive kynureninases preferentially catalyze the hydrolytic cleavage of 3-hydroxy-l-kynurenine to produce 3-hydroxyanthranilate and l-alanine, while l-kynurenine is the substrate of many prokaryotic inducible kynureninases. The human enzyme was cloned with an N-terminal hexahistidine tag, expressed, and purified from a bacterial expression system using Ni metal ion affinity chromatography. Kinetic characterization of the recombinant enzyme reveals classic Michaelis-Menten behavior, with a Km of 28.3 +/- 1.9 microM and a specific activity of 1.75 micromol min-1 mg-1 for 3-hydroxy-dl-kynurenine. Crystals of recombinant kynureninase that diffracted to 2.0 A were obtained, and the atomic structure of the PLP-bound holoenzyme was determined by molecular replacement using the Pseudomonas fluorescens kynureninase structure (PDB entry 1qz9) as the phasing model. A structural superposition with the P. fluorescens kynureninase revealed that these two structures resemble the "open" and "closed" conformations of aspartate aminotransferase. The comparison illustrates the dynamic nature of these proteins' small domains and reveals a role for Arg-434 similar to its role in other AAT alpha-family members. Docking of 3-hydroxy-l-kynurenine into the human kynureninase active site suggests that Asn-333 and His-102 are involved in substrate binding and molecular discrimination between inducible and constitutive kynureninase substrates.
Project description:The tumor suppressor protein RB acts as a transcription repressor via the interaction of its pocket domain with an L/IXCXE motif in HDAC proteins such as HDAC1. Here we demonstrated that while lacking an L/IXCXE motif, HDAC5 interacts with both RB-N (via an FXXXV motif) and RB-C segments and this interaction is diminished by RB serine-249/threonine-252 and threonine-821 phosphorylation. HDAC5 gene is frequently downregulated or deleted in human cancers such as prostate cancer. Loss of HDAC5 increases histone H3 lysine 27 acetylation (H3K27-ac) and circumvents RB-mediated repression of cell cycle-related oncogenic genes. Accordingly, HDAC5 loss confers resistance to the CDK4/6 inhibitors such as Palbociclib in prostate cancer cells in vitro and in mice, but this effect is overcome by the BET-CBP/p300 dual inhibitor NEO2734. Our findings reveal an unknown role of HDAC5 in RB-mediated histone deacetylation and gene repression and a mechanism modulating CDK4/6 inhibitor therapeutic sensitivity in cancer cells.