c-Abl tyrosine kinase activates p21 transcription via interaction with p53

c-Abl-TWIST1 Epigenetically Dysregulate Inflammatory Responses during Mycobacterial Infection by Co-Regulating Bone Morphogenesis Protein and miR27a

Mycobacteria propelled modulation of host responses is of considerable interest in the face of emerging drug resistance. Although it is known that Abl tyrosine kinases affect entry and persistence of mycobacteria, mechanisms that couple c-Abl to proximal signaling pathways during immunity are poorly understood. Loss-of-function of c-Abl through Imatinib, in a mouse model of tuberculosis or RNA interference, identified bone morphogenesis protein (BMP) signaling as its cellular target. We demonstrate that c-Abl promotes mycobacterial survival through epigenetic modification brought about by KAT5-TWIST1 at Bmp loci. c-Abl-BMP signaling deregulated iNOS, aggravating the inflammatory balance. Interestingly, BMP signaling was observed to have far-reaching effects on host immunity, as it attenuated TLR3 pathway by engaging miR27a. Significantly, these events were largely mediated via WhiB3 and DosR/S/T but not SecA signaling pathway of mycobacteria. Our findings suggest molecular mechanisms of host pathways hijacked by mycobacteria and expand our understanding of c-Abl inhibitors in potentiating innate immune responses.

Stabilization of the p53-DNA Complex by the Nuclear Protein Dmp1α

We recently reported the existence of a physical interaction between the Myb-like transcription factor Dmp1 (Dmtf1) and p53 in which Dmp1 antagonized polyubiquitination of p53 by Mdm2 and promoted its nuclear localization. Dmp1 significantly stabilized p53-DNA complexes on promoters that contained p53-consensus sequences, which were either supershifted or disrupted with antibodies to Dmp1. Lysates from mice injected with doxorubicin showed that Dmp1 bound to p21Cip1, Bbc3, and Thbs1 gene regulatory regions in a p53-dependent fashion. Our data suggest that acceleration of DNA-binding of p53 by Dmp1 is a critical process for Dmp1 to increase the p53 function in Arf-deficient cells.

Inhibition of MDM2 by nilotinib contributes to cytotoxicity in both Philadelphia-positive and negative acute lymphoblastic leukemia

Nilotinib is a selective BCR-ABL tyrosine kinase inhibitor related to imatinib that is more potent than imatinib. Nilotinib is widely used to treat chronic myelogenous leukemia (CML) and Philadelphia-positive (Ph+) acute lymphoblastic leukemia (ALL). The present study identifies Mouse double minute 2 homolog (MDM2) as a target of nilotinib. In studying ALL cell lines, we found that the expression of MDM2 in both Philadelphia positive (Ph+) and Philadelphia negative (Ph-) ALL cells was remarkably inhibited by nilotinib, in a dose- and time-dependent manner. Further studies demonstrated that nilotinib inhibited MDM2 at the post-translational level by inducing MDM2 self-ubiquitination and degradation. Nilotinib-mediated MDM2 downregulation did not result in accumulation and activation of p53. Inhibition of MDM2 in nilotinib-treated ALL cells led to downregulation of the anti-apoptotic protein X-linked inhibitor of apoptosis protein (XIAP), a translational target of MDM2, resulting in activation of caspases. Inhibition of XIAP following nilotinib-mediated downregulation of MDM2 resulted in apoptosis of MDM2-expressing ALL; however, similar nilotinib treatment induced stronger apoptosis in Ph+/MDM2+ ALL than in Ph-/MDM2+ or Ph+/MDM2- ALL. The ALL cells that were Ph-/MDM2- were totally resistant to nilotinib. These results suggested that nilotinib can inhibit MDM2 and induce a p53-independent apoptosis pathway by downregulating XIAP; thus, nilotinib can treat not only Ph+, but also Ph- ALL patients whose cancer cells overexpress MDM2.

Kinase-independent mechanisms of resistance of leukemia stem cells to tyrosine kinase inhibitors

Tyrosine kinase inhibitors such as imatinib mesylate have changed the clinical course of chronic myeloid leukemia; however, the observation that these inhibitors do not target the leukemia stem cell implies that patients need to maintain lifelong therapy. The mechanism of this phenomenon is unclear: the question of whether tyrosine kinase inhibitors are inactive inside leukemia stem cells or whether leukemia stem cells do not require breakpoint cluster region (Bcr)-Abl signaling is currently under debate. Herein, I propose an alternative model: perhaps the leukemia stem cell requires Bcr-Abl, but is dependent on its kinase-independent functions. Kinases such as epidermal growth factor receptor and Janus kinase 2 possess kinase-independent roles in regulation of gene expression; it is worth investigating whether Bcr-Abl has similar functions. Mechanistically, Bcr-Abl is able to activate the Ras, phosphatidylinositol 3-kinase/Akt, and/or the Src-kinase Hck/Stat5 pathways in a scaffolding-dependent manner. Whereas the scaffolding activity of Bcr-Abl with Grb2 is dependent on autophosphorylation, kinases such as Hck can use Bcr-Abl as substrate, inducing phosphorylation of Y177 to enable scaffolding ability in the absence of Bcr-Abl catalytic activity. It is worth investigating whether leukemia stem cells exclusively express kinases that are able to use Bcr-Abl as substrate. A kinase-independent role for Bcr-Abl in leukemia stem cells would imply that drugs that target Bcr-Abl's scaffolding ability or its DNA-binding ability should be used in conjunction with current therapeutic regimens to increase their efficacy and eradicate the stem cells of chronic myeloid leukemia.

c-ABL tyrosine kinase modulates p53-dependent p21 induction and ensuing cell fate decision in response to DNA damage

The c-ABL non-receptor tyrosine kinase and the p53 tumor suppressor protein are pivotal modulators of cellular responses to DNA damage. However, a comprehensive understanding of the role of c-ABL kinase in p53-dependent transcription of p21(CIP1/WAF1) and ensuing cell fate decision is still obscure. Here, we demonstrate that c-ABL tyrosine kinase regulates p53-dependent induction of p21. As a result, it modulates cell fate decision by p53 in response to DNA damage differently according to the extent of DNA damage. When human cancer cells were treated with DNA damaging agent, adriamycin (0.08 μg/ml), p21 was induced following p53 induction. Owing largely to p21, a substantial fraction of cells treated with adriamycin were blocked at the G2 phase of the cell cycle and most cells eventually became senescent. When these cells were simultaneously treated with a c-ABL kinase inhibitor, STI571, or a c-ABL-specific siRNA along with adriamycin, the p53-dependent p21 induction was dramatically diminished, even though p53 is substantially induced. Accordingly, G2-arrest, and cellular senescence largely dependent on p21 were substantially abrogated. On the contrary, when cells were treated with a relatively high dose of adriamycin (0.4 μg/ml) cells became apoptotic, and the simultaneous presence of a c-ABL kinase inhibitor STI571 augmented the extent of apoptosis. We speculate this is due to abrogation of p53-dependent p21 induction, which leads to elimination of anti-apoptotic function of p21. In summary, c-ABL appears to promote senescence or inhibit apoptosis, depending on the extent of DNA damage. These findings suggest that the combined use of ABL kinase inhibitor and DNA damaging drug in chemotherapy against tumors retaining wild type p53 should be carefully designed.

CSF1R signaling blockade stanches tumor-infiltrating myeloid cells and improves the efficacy of radiotherapy in prostate cancer

Radiotherapy is used to treat many types of cancer, but many treated patients relapse with local tumor recurrence. Tumor-infiltrating myeloid cells (TIM), including CD11b (ITGAM)(+)F4/80 (EMR1)+ tumor-associated macrophages (TAM), and CD11b(+)Gr-1 (LY6G)+ myeloid-derived suppressor cells (MDSC), respond to cancer-related stresses and play critical roles in promoting tumor angiogenesis, tissue remodeling, and immunosuppression. In this report, we used a prostate cancer model to investigate the effects of irradiation on TAMs and MDSCs in tumor-bearing animals. Unexpectedly, when primary tumor sites were irradiated, we observed a systemic increase of MDSCs in spleen, lung, lymph nodes, and peripheral blood. Cytokine analysis showed that the macrophage colony-stimulating factor CSF1 increased by two-fold in irradiated tumors. Enhanced macrophage migration induced by conditioned media from irradiated tumor cells was completely blocked by a selective inhibitor of CSF1R. These findings were confirmed in patients with prostate cancer, where serum levels of CSF1 increased after radiotherapy. Mechanistic investigations revealed the recruitment of the DNA damage-induced kinase ABL1 into cell nuclei where it bound the CSF1 gene promoter and enhanced CSF1 gene transcription. When added to radiotherapy, a selective inhibitor of CSF1R suppressed tumor growth more effectively than irradiation alone. Our results highlight the importance of CSF1/CSF1R signaling in the recruitment of TIMs that can limit the efficacy of radiotherapy. Furthermore, they suggest that CSF1 inhibitors should be evaluated in clinical trials in combination with radiotherapy as a strategy to improve outcomes.

Towards inferring time dimensionality in protein-protein interaction networks by integrating structures: the p53 example

Structural data, efficient structural comparison algorithms and appropriate datasets and filters can assist in getting an insight into time dimensionality in interaction networks; in predicting which interactions can and cannot co-exist; and in obtaining concrete predictions consistent with experiment.

Inspection of protein–protein interaction maps illustrates that a hub protein can interact with a very large number of proteins, reaching tens and even hundreds. Since a single protein cannot interact with such a large number of partners at the same time, this presents a challenge: can we figure out which interactions can occur simultaneously and which are mutually excluded? Addressing this question adds a fourth dimension into interaction maps: that of time. Including the time dimension in structural networks is an immense asset; time dimensionality transforms network node-and-edge maps into cellular processes, assisting in the comprehension of cellular pathways and their regulation. While the time dimensionality can be further enhanced by linking protein complexes to time series of mRNA expression data, current robust, network experimental data are lacking. Here we outline how, using structural data, efficient structural comparison algorithms and appropriate datasets and filters can assist in getting an insight into time dimensionality in interaction networks; in predicting which interactions can and cannot co-exist; and in obtaining concrete predictions consistent with experiment. As an example, we present p53-linked processes.

Identification of retinoic acid-regulated nuclear matrix-associated protein as a novel regulator of gastric cancer

BACKGROUND

Retinoic acid-regulated nuclear matrix-associated protein (RAMP) is a WD40 repeat-containing protein that is involved in various biological functions, but little is known about its role in human cancer. This study aims to delineate the oncogenic role of RAMP in gastric carcinogenesis.

METHODS

RAMP expression was examined by real-time quantitative RT-PCR, immunohistochemistry and western blotting. Inhibition of RAMP expression was performed by siRNA-mediated knockdown. The functional effects of RAMP on cell kinetics were measured by cell viability assay, colony formation assay and flow cytometry. Cell lines stably expressing RAMP were established to investigate the oncogenic effects of RAMP in vitro.

RESULTS

Ramp was readily expressed in all seven gastric cancer cell lines and was significantly increased in human gastric cancer tissues when compared with their adjacent non-cancerous tissues (P<0.001). In keeping with this, expression of RAMP protein was higher in gastric cancer tissues compared with their adjacent non-cancerous tissues, whereas moderate protein expression were noted in intestinal metaplasia. Knockdown of RAMP in gastric cancer cells significantly reduced cell proliferation (P<0.01) and soft agar colony formation (P<0.001), but induced apoptosis and G(2)/M arrest. In additional, knockdown RAMP induced cell apoptosis is dependent on functional accumulation of p53 and p21 and induction of cleaved caspases-9, caspases-3 and PARP. Strikingly, overexpression of RAMP promoted anchorage-independent cell growth in soft agar.

CONCLUSION

Our findings demonstrate that RAMP plays an oncogenic role in gastric carcinogenesis. Inhibition of RAMP may be a promising approach for gastric cancer therapy.

mTOR inhibitor RAD001 (Everolimus) enhances the effects of imatinib in chronic myeloid leukemia by raising the nuclear expression of c-ABL protein

Constitutive tyrosine kinase (TK) activity of p210 BCR-ABL fusion protein of chronic myeloid leukemia (CML) usurps physiological functions of normal p145 c-ABL protein. Accordingly, its inhibition by imatinib mesylate (IM) lets p145 c-ABL translocate into the nuclear compartment, which drives cell growth arrest and apoptotic death. Here we show that IM and the mammalian target of rapamycin (mTOR) inhibitor RAD001 (Everolimus) have additive effects on BCR-ABL-expressing cells. Those effects are at least partly conditional upon the enhanced nuclear accumulation of p145 c-ABL through events encompassing post-translational modifications of p145 c-ABL (Thr(735) phosphorylation) precluding its nuclear export and of 14-3-3 sigma (Ser(186) phosphorylation by c-Jun N-terminal kinase [JNK]) promoting p145 c-ABL nuclear re-import.

L-selectin ligation-induced CSF-1 gene transcription is regulated by AP-1 in a c-Abl kinase-dependent manner

L-selectin is a cell adhesion molecule that plays an important role both in mediating the initial capture and subsequent rolling of leukocytes along the endothelial cells and in the signal transduction for leukocyte activation. In our previous studies, we reported that L-selectin ligation could increase macrophage colony-stimulating factor (CSF)-1 gene transcription, in which c-Abl acts as a crucial cytoplasmic kinase. Here we investigated the function of the nuclear c-Abl kinase in the CSF-1 gene transcriptional events triggered by L-selectin ligation. We determined that c-Abl kinase recruits to the nucleus following L-selectin ligation, and the nuclear c-Abl kinase can phosphorylate c-Jun and regulate activator protein (AP)-1 activity. Furthermore, the activated c-Abl kinase interacts with AP-1 and forms a complex in the CSF-1 promoter region to regulate CSF-1 gene transcription in the L-selectin ligation-activated cells. These results indicate that nuclear c-Abl kinase can activate CSF-1 gene transcription by regulating AP-1 activity in the signaling events induced by L-selectin ligation.