Puthiyaveettil N. Raghunath

Oncogenic kinase NPM/ALK induces through STAT3 expression of immunosuppressive protein CD274 (PD-L1, B7-H1)

The mechanisms of malignant cell transformation caused by the oncogenic, chimeric nucleophosmin (NPM)/anaplastic lymphoma kinase (ALK) remain only partially understood, with most of the previous studies focusing mainly on the impact of NPM/ALK on cell survival and proliferation. Here we report that the NPM/ALK-carrying T cell lymphoma (ALK+TCL) cells strongly express the immunosuppressive cell-surface protein CD274 (PD-L1, B7-H1), as determined on the mRNA and protein level. The CD274 expression is strictly dependent on the expression and enzymatic activity of NPM/ALK, as demonstrated by inhibition of the NPM/ALK function in ALK+TCL cells by the small molecule ALK inhibitor CEP-14083 and by documenting CD274 expression in IL-3-depleted BaF3 cells transfected with the wild-type NPM/ALK, but not the kinase-inactive NPM/ALK K210R mutant or empty vector alone. NPM/ALK induces CD274 expression by activating its key signal transmitter, transcription factor STAT3. STAT3 binds to the CD274 gene promoter in vitro and in vivo, as shown in the gel electromobility shift and chromatin immunoprecipitation assays, and is required for the PD-L1 gene expression, as demonstrated by siRNA-mediated STAT3 depletion. These findings identify an additional cell-transforming property of NPM/ALK and describe a direct link between an oncoprotein and an immunosuppressive cell-surface protein. These results also provide an additional rationale to therapeutically target NPM/ALK and STAT3 in ALK+TCL. Finally, they suggest that future immunotherapeutic protocols for this type of lymphoma may need to include the inhibition of NPM/ALK and STAT3 to achieve optimal clinical efficacy.

Lack of Phosphotyrosine Phosphatase SHP-1 Expression in Malignant T-Cell Lymphoma Cells Results from Methylation of the SHP-1 Promoter

SHP-1 is an important negative regulator of signaling by several receptors including receptors for interleukin-2 (IL-2R) and other cytokines. SHP-1 acts by dephosphorylating the receptors and receptor-associated kinases such as IL-2R-associated Jak3 kinase. We found that SHP-1 protein was not detectable or greatly diminished in most (six of seven) T cell lines derived from various types of T cell lymphomas and all (eight of eight) cutaneous T-cell lymphoma tissues with a transformed, large-cell morphology. All T-cell lymphoma lines tested (eight of eight) expressed diminished amounts or no detectable SHP-1 mRNA. These T cell lines did not, however, carry any mutations in the SHP-1 gene-coding, splice-junction, and promoter regions. Importantly, SHP-1 DNA promoter region in the T cell lines was resistant to digestion with three different methylation-sensitive restriction enzymes. This resistance was reversed by treatment of the cells with a demethylating agent, 5-deoxyazacytidine. The treatment resulted also in the expression of SHP-1 mRNA and, less frequently, SHP-1 protein. The expression of SHP-1 protein was associated with dephosphorylation of the Jak3 kinase. These results show that lack of SHP-1 expression is frequent in malignant T cells and results from methylation of the SHP-1 gene promoter. Furthermore, they indicate that SHP-1 loss may play a role in the pathogenesis of T cell lymphomas by permitting persistence of signals generated by IL-2R and, possibly, other receptor complexes.

Plasminogen Activator System in Human Coronary Atherosclerosis

Altered coronary artery expression of plasminogen activator (PA) system components may predispose to thrombosis and modulate the vascular response to injury. By immunohistochemistry, we studied the expression of PAs (tPA and uPA), their major physiological inhibitor (PAI-1), and a receptor for uPA (uPAR) in human coronary arteries with either pure fibrointimal proliferation (n = 15) or developed atherosclerotic plaques (n = 10). Overall, the degree of staining showed the following rank order: PAI-1 > tPA > uPAR > uPA. A similar pattern was seen in two normal coronary arteries. There were no significant differences in the extent of staining in any vascular compartment between atherosclerotic arteries and those with only fibrointimal proliferation. However, the ratio of intimal to medial expression of tPA (P = .001) and uPAR (P = .004) was significantly increased in atherosclerotic arteries, with a similar trend for uPA (P = .069) but not for PAI-1 (P = .73). Four of 10 atherosclerotic arteries had higher uPAR expression in the intima than in the media, whereas none of the 15 arteries with only fibrointimal proliferation had this pattern (P < .01). Dual labeling studies demonstrated colocalization of all four PA system components in endothelial cells, smooth muscle cells, and macrophages, with a predominance of PAI-1. Thus, coronary arteries with a wide range of vascular pathology express an abundance of antifibrinolytic potential with enhanced local expression of profibrinolytic proteins, mainly within atherosclerotic plaques.

Oncogenic tyrosine kinase NPM/ALK induces activation of the rapamycin-sensitive mTOR signaling pathway

The mechanisms of cell transformation mediated by the nucleophosmin (NPM)/anaplastic lymphoma kinase (ALK) tyrosine kinase are only partially understood. Here, we report that cell lines and native tissues derived from the NPM/ALK-expressing T-cell lymphoma display persistent activation of mammalian target of rapamycin (mTOR) as determined by phosphorylation of mTOR targets S6rp and 4E-binding protein 1 (4E-BP1). The mTOR activation is serum growth factor-independent but nutrient-dependent. It is also dependent on the expression and enzymatic activity of NPM/ALK as demonstrated by cell transfection with wild-type and functionally deficient NPM/ALK, small interfering RNA (siRNA)-mediated NPM/ALK depletion and kinase activity suppression using the inhibitor WHI-P154. The NPM/ALK-induced mTOR activation is transduced through the mitogen-induced extracellular kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathway and, to a much lesser degree, through the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway. Accordingly, whereas the low-dose PI3K inhibitor wortmannin and Akt inhibitor III profoundly inhibited Akt phosphorylation, they had a very modest effect on S6rp and 4E-BP1 phosphorylation. In turn, MEK inhibitors U0126 and PD98059 and siRNA-mediated depletion of either ERK1 or ERK2 inhibited S6rp phosphorylation much more effectively. Finally, the mTOR inhibitor rapamycin markedly decreased proliferation and increased the apoptotic rate of ALK+TCL cells. These findings identify mTOR as a novel key target of NPM/ALK and suggest that mTOR inhibitors may prove effective in therapy of ALK-induced malignancies.

Differential Expression of Functional Protease-Activated Receptor-2 (PAR-2) in Human Vascular Smooth Muscle Cells

The protease-activated family of G protein-coupled receptors includes PAR-1 and PAR-3, which are activated by thrombin, and PAR-2, which is activated by trypsin and tryptase. PAR-2 has recently been shown to be expressed in human endothelial cells. In the present studies, we have examined the expression of PAR-2 in other cells, particularly vascular smooth muscle, and tested whether the receptors are functional. The results show that PAR-2 is present in human aorta and coronary artery smooth muscle cells, as well as in arteries traversing the walls of the small intestine. It was also detected in human keratinocytes, sweat glands, intestinal smooth muscle, and intestinal epithelium, but not at all in myocardial smooth muscle and only inconsistently in intestinal veins and venules. Activation of aortic smooth muscle cells in culture with PAR-2 peptide agonists caused a transient increase in the cytosolic Ca2+ concentration. In contrast, PAR-2 mRNA could not be detected in saphenous vein smooth muscle cells, and the same cells placed in culture showed little, if any, response to the PAR-2 agonist peptides. These observations show that PAR-2 is widely distributed in human vascular smooth muscle, particularly in arteries. However, this is not a universal finding and at least some venous smooth muscle cells, including those in saphenous veins, apparently do not express the receptor in detectable amounts.

Oncogenic tyrosine kinase NPM/ALK induces activation of the MEK/ ERK signaling pathway independently of c-Raf

The mechanisms of cell transformation mediated by the highly oncogenic, chimeric NPM/ALK tyrosine kinase remain only partially understood. Here we report that cell lines and native tissues derived from the NPM/ALK-expressing T-cell lymphoma (ALK+ TCL) display phosphorylation of the extracellular signal-regulated protein kinase (ERK) 1/2 complex. Transfection of BaF3 cells with NPM/ALK induces phosphorylation of EKR1/2 and of its direct activator mitogen-induced extracellular kinase (MEK) 1/2. Depletion of NPM/ALK by small interfering RNA (siRNA) or its inhibition by WHI-154 abrogates the MEK1/2 and ERK1/2 phosphorylation. The NPM/ALK-induced MEK/ERK activation is independent of c-Raf as evidenced by the lack of MEK1/2 and ERK1/2 phosphorylation upon c-Raf inactivation by two different inhibitors, RI and ZM336372, and by its siRNA-mediated depletion. In contrast, ERK1/2 activation is strictly MEK1/2 dependent as shown by suppression of the ERK1/2 phosphorylation by the MEK1/2 inhibitor U0126. The U0126-mediated inhibition of ERK1/2 activation impaired proliferation and viability of the ALK+ TCL cells and expression of antiapoptotic factor Bcl-xL and cell cycle-promoting CDK4 and phospho-RB. Finally, siRNA-mediated depletion of both ERK1 and ERK2 inhibited cell proliferation, whereas depletion of ERK 1 (but not ERK2) markedly increased cell apoptosis. These findings identify MEK/ERK as a new signaling pathway activated by NPM/ALK and indicate that the pathway represents a novel therapeutic target in the ALK-induced malignancies.

Nek3 kinase regulates prolactin-mediated cytoskeletal reorganization and motility of breast cancer cells

Prolactin (PRL) stimulates the cytoskeletal re-organization and motility of breast cancer cells. During PRL receptor signaling, Vav2 becomes phosphorylated and activated, an event regulated by the serine/threonine kinase Nek3. Given the regulatory role of Vav2, the function of Nek3 in PRL-mediated motility and invasion was examined. Overexpression of Nek3 in Chinese hamster ovary transfectants potentiated cytoskeletal re-organization in response to PRL. In contrast, downregulation of Nek3 expression by small-interfering RNA (siRNA) attenuated PRL-mediated cytoskeletal reorganization, activation of GTPase Rac1, cell migration and invasion of T47D cells. In addition, PRL stimulation induced an interaction between Nek3 and paxillin and significantly increased paxillin serine phosphorylation, whereas Nek3 siRNA-transfected cells showed a marked reduction in paxillin phosphorylation. Analysis of breast tissue microarrays also demonstrated a significant up-regulation of Nek3 expression in malignant versus normal specimens. These data suggest that Nek3 contributes to PRL-mediated breast cancer motility through mechanisms involving Rac1 activation and paxillin phosphorylation.

Expression patterns of the immunosuppressive proteins PD-1/CD279 and PD-L1/CD274 at different stages of cutaneous T-cell lymphoma/mycosis fungoides.

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Stabilization of prolactin receptor in breast cancer cells

The role of the hormone prolactin (PRL) in the pathogenesis of breast cancer is mediated by its cognate receptor (PRLr). Ubiquitin-dependent degradation of the PRLr that negatively regulates PRL signaling is triggered by PRL-mediated phosphorylation of PRLr on Ser349 followed by the recruitment of the beta-transducin repeats-containing protein (β-TrCP) ubiquitin-protein isopeptide ligase. We report here for the first time that interaction between PRLr and β-TrCP is less efficient in human breast cancer cells than in non-tumorigenic human mammary epithelial cells. Furthermore, we demonstrate that both PRLr degradation and PRLr phosphorylation on Ser349 are impaired in breast tumor cells and tissues, an observation that directly correlates with enhanced expression of the PRLr in malignant breast epithelium. These findings represent a novel mechanism through which altered PRLr stability may directly influence the pathogenesis of breast cancer.

Constitutive activation of mTOR signaling pathway in post-transplant lymphoproliferative disorders

We examined activation of the mTOR signaling pathway in situ in the primary, normal reactive and patient-derived post-transplant lymphoproliferative disorder (PTLD) tissue samples. We accomplished this analysis by immunohistochemistry on formalin-fixed, paraffin-embedded specimens using a set of highly specific antibodies that permitted us to determine phosphorylation status of the key serines in the mTOR target proteins. Our results demonstrate that the mTOR signaling pathway is activated in reactive tissue in a highly distinct fashion with positive, typically enlarged cells being present primarily in the germinal center and, to a lesser degree, in interfollicular areas with mantle zone being conspicuously negative. We could demonstrate mTOR activation in the lesional cells in the entire spectrum of PTLD subtypes, regardless of their Epstein–Barr virus genome expression status. These data demonstrate the ubiquitous activation of the mTOR signaling pathway in PTLD and indicate that mTOR inhibitors may be effective in treatment and, notably, prevention of PTLDs given their immunosuppressive properties. Furthermore, our results define potential biomarkers of the therapeutic response. Because the constitutive mTOR activation has also been identified in cells isolated from other hematologic malignancies, the ability to examine the in vivo mTOR signaling may have implications reaching beyond the PTLD field.