Mirk kinase inhibition blocks the in vivo growth of pancreatic cancer cells.

The Mirk/dyrk1B gene is upregulated and sometimes amplified in pancreatic ductal carcinomas. In poor microenvironmental conditions Mirk mediates cell survival by maintaining cancer cells in a largely quiescent, noncycling state and by decreasing toxic ROS levels through maintaining expression of a series of antioxidant genes. Premature entry into cycle, increased ROS levels, DNA damage, and apoptosis follow Mirk kinase depletion or inhibition.

Mirk kinase inhibition targets ovarian cancer ascites.

The Mirk/dyrk1B gene is commonly amplified or upregulated in ovarian cancers, and Mirk is an active kinase in these cancers. Mirk mediates cancer cell survival by decreasing toxic ROS levels through maintaining expression of a series of antioxidant genes, possibly through its transcriptional activator functions. Mirk has the unusual property of being most active in quiescent cancer cells because of marked transcriptional downregulation by Akt/mTOR signaling and by MEK/erk signaling in cycling cells.

The normal function of the cancer kinase Mirk/dyrk1B is to reduce reactive oxygen species.

Mirk kinase is a gene upregulated and sometimes amplified in pancreatic cancers and in ovarian cancers, but expressed at very low levels in most normal diploid cells except for skeletal muscle. The muscle cell function of Mirk kinase selected for by cancer cells is unknown. It is now shown that Mirk protein is expressed at low levels and is largely nuclear in cycling skeletal muscle C2C12 myoblasts, but is translocated to the cytoplasm and upregulated when myoblasts initiate differentiation, as shown by immunofluorescence staining and by cell fractionation.

Mirk/dyrk1B kinase is upregulated following inhibition of mTOR.

The PI3K/PTEN/Akt/mTOR/p70S6K pathway is one of the most frequently deregulated signaling pathways in solid tumors and has a functional role in drug resistance. However, targeting this pathway leads to compensatory activation of several mediators of cell survival. Expression of the reactive oxygen species-controlling kinase Mirk/dyrk1B was increased severalfold by the mammalian target of rapamycin (mTOR) inhibitors RAD001, WYE354 and rapamycin, with less effect by the Akt inhibitors AZD5363 and MK-2206.

Mirk/dyrk1B Kinase in Ovarian Cancer.

Mirk/dyrk1B kinase is expressed in about 75% of resected human ovarian cancers and in most ovarian cancer cell lines with amplification in the OVCAR3 line. Mirk (minibrain-related kinase) is a member of the Minibrain/dyrk family of related serine/threonine kinases. Mirk maintains cells in a quiescent state by stabilizing the CDK inhibitor p27 and by inducing the breakdown of cyclin D isoforms.

Ovarian cancer cells, not normal cells, are damaged by Mirk/Dyrk1B kinase inhibition.

Prior studies had shown that the Mirk/dyrk1B gene is amplified/upregulated in about 75% of ovarian cancers, that protein levels of this kinase are elevated in quiescent G0 cells and that Mirk maintains tumor cells in quiescence by initiating rapid degradation of cyclin D isoforms and by phosphorylation of a member of the DREAM complex. Depletion of Mirk/dyrk1B led to increased cyclin D levels, an elevated reactive oxygen species (ROS) content and loss of viability. However, many normal cells in vivo are quiescent, and therefore, targeting a kinase found in quiescent cells might be problematic.

Inactivation of mirk/dyrk1b kinase targets quiescent pancreatic cancer cells.

A major problem in the treatment of cancer arises from quiescent cancer cells that are relatively insensitive to most chemotherapeutic drugs and radiation. Such residual cancer cells can cause tumor regrowth or recurrence when they reenter the cell cycle. Earlier studies showed that levels of the serine/theronine kinase Mirk/dyrk1B are elevated up to 10-fold in quiescent G(0) tumor cells.

The role of mirk kinase in sarcomas.

Targeting the tyrosine kinase KIT in gastrointestinal stromal tumors has led to improved treatment. Other kinases might serve as therapeutic targets in the more common forms of sarcoma. The kinase Mirk/dyrk1B is highly expressed in the vast majority of osteosarcomas and rhabdomyosarcomas and mediates their growth, as depletion of Mirk led to tumor cell apoptosis.

Depleting Mirk Kinase Increases Cisplatin Toxicity in Ovarian Cancer Cells.

Cisplatin-based regimens are the standard of care for epithelial carcinoma of the ovary. Since cisplatin is known to increase intracellular levels of toxic reactive oxygen species (ROS), an increase in cisplatin toxicity selectively in cancer cells could result from further increasing the cisplatin-elevated ROS levels by targeting antioxidant genes upregulated in ovarian cancers. The serine/threonine kinase Mirk/dyrk1B is a transcriptional co-activator which increased the expression of the antioxidant genes superoxide dismutase 2 and ferroxidase in ovarian cancer cells.

Transient arrest in a quiescent state allows ovarian cancer cells to survive suboptimal growth conditions and is mediated by both Mirk/dyrk1b and p130/RB2.

Some ovarian cancer cells in vivo are in a reversible quiescent state where they can contribute to cancer spread under favorable growth conditions. The serine/threonine kinase Mirk/dyrk1B was expressed in each of seven ovarian cancer cell lines and in 21 of 28 resected human ovarian cancers, and upregulated in 60% of the cancers. Some ovarian cancer cells were found in a G0 quiescent state, with the highest fraction in a line with an amplified Mirk gene.

The Kinase Mirk/dyrk1B: A Possible Therapeutic Target in Pancreatic Cancer.

Pancreatic ductal adenocarcinomas are strongly resistant to chemotherapeutic drugs and radiation, underscoring the need for new therapeutic targets, particularly ones which target the numerous out of cycle cancer cells. Analysis of resected tumors for nuclear Ki67 antigen has shown that about 70% of pancreatic cancer cells are out of cycle, some post-mitotic. Other out of cycle cells are in a quiescent, reversible G0 state, resistant to drugs which target dividing cells, with some able to repopulate a tumor.

Mirk regulates the exit of colon cancer cells from quiescence.

Mirk/Dyrk1B is a serine/threonine kinase widely expressed in colon cancers. Serum starvation induced HD6 colon carcinoma cells to enter a quiescent G0 state, characterized by a 2N DNA content and a lower RNA content than G1 cells. Compared with cycling cells, quiescent cells exhibited 16-fold higher levels of the retinoblastoma protein p130/Rb2, which sequesters E2F4 to block entry into G1, 10-fold elevated levels of the CDK inhibitor p27kip1, and 10-fold higher levels of Mirk.

Mirk/Dyrk1B maintains the viability of quiescent pancreatic cancer cells by reducing levels of reactive oxygen species.

The kinase Mirk/dyrk1B mediated the clonogenic growth of pancreatic cancer cells in earlier studies. It is now shown that Mirk levels increased 7-fold in SU86.86 pancreatic cancer cells when over a third of the cells were accumulated in a quiescent G(0) state, defined by Hoechst/Pyronin Y staining.

The survival kinase Mirk/Dyrk1B is a downstream effector of oncogenic K-ras in pancreatic cancer.

The kinase Mirk is overexpressed in many resected pancreatic adenocarcinomas and is amplified in a subset of pancreatic cancer cell lines. Depletion of Mirk has been shown to lead to apoptosis in pancreatic cancer cell lines, and thus to inhibit their clonogenic growth. Mirk is activated by signaling from activated Rac1 to MKK3 in MDCK cells, but the mechanism of activation of Mirk in pancreatic cancers is unknown.

Mirk/Dyrk1B in cancer.

Mirk/Dyrk1B is a member of a conserved family of serine/threonine kinases which are activated by intramolecular tyrosine phosphorylation, and which mediate differentiation in different tissues-Mirk in skeletal muscle, Dyrk1A in the brain, etc. One role of Mirk in skeletal muscle differentiation is to block cycling myoblasts in the G0 quiescent state by modification of cell cycle regulators, while another role of Mirk is to limit apoptosis in fusing myoblasts. Amplification of the Mirk gene, upregulation of Mirk expression and/or constitutive activation of this kinase have been observed in several different types of cancer.

Mirk/Dyrk1B: a multifunctional dual-specificity kinase involved in growth arrest, differentiation, and cell survival.

Minibrain-related kinase (Mirk)/dual-specificity tyrosine-regulated kinase (Dyrk)1B is one of the best functionally characterized members of the Dyrk/Minibrain family of dual-specificity kinases. Dyrk family kinases are highly conserved mediators of growth control and differentiation. Mirk is expressed at high levels in skeletal muscle; thus, most of the recent studies of Mirk have used myogenesis as a model system to explore the function of Mirk in a native physiological environment.

Mirk/Dyrk1b mediates cell survival in rhabdomyosarcomas.

Rhabdomyosarcoma is the most common sarcoma in children and is difficult to treat if the primary tumor is nonresectable or if the disease presents with metastases. The function of the serine/threonine kinase Mirk was investigated in this cancer. Mirk has both growth arrest and survival functions in terminally differentiating skeletal myoblasts.

The kinase Mirk/Dyrk1B mediates cell survival in pancreatic ductal adenocarcinoma.

Ductal adenocarcinoma of the pancreas is almost uniformly lethal as this cancer is invariably detected at an advanced stage and is resistant to treatment. The serine/threonine kinase Mirk/Dyrk1B has been shown to be antiapoptotic in rhabdomyosarcomas. We have now investigated whether Mirk might mediate survival in another cancer in which Mirk is widely expressed, pancreatic ductal adenocarcinoma.

The survival kinase Mirk/dyrk1B is activated through Rac1-MKK3 signaling.

The serine/threonine kinase Mirk/dyrk1B is activated in several solid tumors where it mediates cell survival, but the mechanism by which Mirk is activated in tumors is unknown. We now demonstrate that Mirk is activated as a kinase by signaling from Rac1 to the mitogen-activated protein kinase kinase MKK3. Rac is a Ras superfamily GTPase that, when activated, functions downstream of Ras oncoproteins to promote cell survival, transformation, and membrane ruffling.

Mirk/Dyrk1B mediates survival during the differentiation of C2C12 myoblasts.

The kinase Mirk/dyrk1B is essential for the differentiation of C2C12 myoblasts. Mirk reinforces the G0/G1 arrest state in which differentiation occurs by directly phosphorylating and stabilizing p27(Kip1) and destabilizing cyclin D1. We now demonstrate that Mirk is anti-apoptotic in myoblasts.

Mirk/dyrk1B decreases the nuclear accumulation of class II histone deacetylases during skeletal muscle differentiation.

Mirk/dyrk1B is a member of the dyrk/minibrain family of serine/threonine kinases that mediate the transition from growth to differentiation in lower eukaryotes and mammals. Depletion of endogenous Mirk from C2C12 myoblasts by RNA interference blocks skeletal muscle differentiation (Deng, X., Ewton, D.

Mirk/dyrk1B kinase destabilizes cyclin D1 by phosphorylation at threonine 288.

The phosphorylation of cyclin D1 at threonine 286 by glycogen synthase kinase 3beta (GSK3beta) has been shown to be required for the ubiquitination and nuclear export of cyclin D1 and its subsequent degradation in the proteasome. The mutation of the nearby residue, threonine 288, to nonphosphorylatable alanine has also been shown to reduce the ubiquitination of cyclin D1, suggesting that phosphorylation at threonine 288 may also lead to degradation of cyclin D1. We now demonstrate that the G(0)/G(1)-active arginine-directed protein kinase Mirk/dyrk1B binds to cyclin D1 and phosphorylates cyclin D1 at threonine 288 in vivo and that the cyclin D1-T288A construct is more stable than wild-type cyclin D1.

The cyclin-dependent kinase inhibitor p27Kip1 is stabilized in G(0) by Mirk/dyrk1B kinase.

Elevated levels of the cyclin-dependent kinase (CDK) inhibitor p27 block the cell in G(0)/G(1) until mitogenic signals activate G(1) cyclins and initiate proliferation. Post-translational regulation of p27 by different phosphorylation events is critical in allowing cells to proceed through the cell cycle. We now demonstrate that the arginine-directed kinase, Mirk/dyrk1B, is maximally active in G(0) in NIH3T3 cells, when it stabilizes p27 by phosphorylating it at Ser-10.

Serine/threonine kinase Mirk/Dyrk1B is an inhibitor of epithelial cell migration and is negatively regulated by the Met adaptor Ran-binding protein M.

Minibrain-related kinase (Mirk)/Dyrk1B is an arginine-directed serine/threonine kinase that is active in skeletal muscle development but is also expressed in various carcinomas. In the current study, the Met adaptor protein Ran-binding protein M (RanBPM) was identified as a Mirk-binding protein by yeast two-hybrid analysis. The Mirk-RanBPM association was confirmed by glutathione S-transferase pull-down assays, co-immunoprecipitation studies, and in vivo cross-linking.

Mirk/dyrk1B is a Rho-induced kinase active in skeletal muscle differentiation.

The Rho family of small GTPases regulates numerous signaling pathways that control the organization of the cytoskeleton, transcription factor activity, and many aspects of the differentiation of skeletal myoblasts. We now demonstrate that the kinase Mirk (minibrain-related kinase)/dyrk1B is induced by members of the Rho-family in myoblasts and that Mirk is active in skeletal muscle differentiation. Mirk is an arginine-directed serine/threonine kinase which is expressed at elevated levels in skeletal muscle compared with other normal tissues.