Invited reviewNovel players in multiple myeloma pathogenesis: Role of protein kinases CK2 and GSK3
Introduction
Multiple myeloma (MM) is a blood tumor arising from terminally differentiated B lymphocytes, plasma cells, which grow mainly in the bone marrow (BM). Due to the progressive accumulation of malignant plasma cells, which produce monoclonal immunoglobulins or parts of them (light chains), end-organ damage often occurs in the bone, in the kidneys and in the bone marrow [1].
Although MM is a fatal disorder, in recent years notable progresses have been achieved in the cure of this disease, mostly due to the introduction of novel and effective drugs in the therapeutic armamentarium. For instance, the discovery that proteasome inhibitors and immunomodulatory drugs (iMIDs) caused MM cell growth arrest and their subsequent clinical employment have changed the clinical outcome of MM patients allowing to obtain a prolongation of the overall survival.
Significant efforts are being carried out in order to identify the cellular and molecular alterations underlying MM pathogenesis. As a consequence, several pre-clinical studies as well as clinical trials have started with the aim of identifying more effective therapeutic combinations able to arrest MM cell growth [2], [3].
It is now well established that malignant plasma cell growth relies on cell intrinsic as well as cell extrinsic or external mechanisms. Since specific genetic lesions are associated with the deregulation of signaling pathways in MM plasma cells [4], based on their characterization it is now possible to prognostically classify MM patients [5]. Overall, a central importance in MM pathogenesis is displayed by perturbations of signaling cascades regulating the balance between cell death and life. For instance, the deregulation of Cyclin Ds, mostly D1 but also D2 and D3, is associated with a specific chromosomal translocation t(11;14) and/or specific genomic alterations. Cyclin Ds over-expression leads to increased cell cycle progression and proliferation. Also, the transcription factors c-Myc is deregulated in a substantial fraction of MM and it seems that malignant plasma cells are addicted to c-Myc over-function. Last, the NF-κB transcription factor signaling pathway is disrupted in approximately 20% of MM cases. Different kind of mutations affecting NF-κB regulating genes altogether may converge on the over-activation of this pro-survival signaling cascade [6].
Another very important pathogenic role is played by the MM microenvironment. In the BM malignant plasma cells take crucial interactions with surrounding hematopoietic and non-hematopoietic (stromal) cells as well as with the extracellular matrix. Contacts between MM cells and the microenvironment support MM cell growth and provide a protective niche against cytotoxic agents. It is increasingly clear that the MM BM microenvironment exhibits distinct alterations, which concur to provide an inflammatory/proangiogenic milieu that in turn favors malignant plasma cell growth [5], [7].
On the way to search for molecules involved in sustaining MM cell growth others’ and our group analyzed the function of two serine-threonine protein kinases, CK2 and GSK3 in MM. These PKs are ubiquitous, regulate several cellular processes and their loss in mice is lethal.
CK2 is mostly a constitutively active kinase, even though also inducible, mainly by stress signals; GSK3, originally identified in the insulin-dependent signaling pathway as the kinase phosphorylating the enzyme glycogen synthase, is a constitutively active kinase, which is shut off in a signal-dependent fashion by upstream cascades, in particular by the PI3K/AKT axis [8], [9].
CK2 and GSK3 share a common feature, i.e. the ability to phosphorylate several transcription factors, many of which are involved in cell proliferation, differentiation and apoptosis. For instance, both CK2 and GSK3 can phosphorylate NF-κB cascade members, promoting the activation of this pathway [10]. CK2 and GSK3 also phosphorylate c-Myc and Myb, causing an increased activity of these transcription factors [11], [12]. CK2 and GSK3 have also been involved in the function of several developmentally regulated hematopoietic-specific transcription factors and chromatin modifiers [13].
Recently, a number of studies have described that both these PKs can promote MM plasma cell growth by affecting critical signaling pathways and cellular mechanisms. We will herein review the current knowledge on the pathogenic roles of CK2 and GSK3 in MM and discuss the possibility of using small selective CK2 and GSK3 inhibitors as therapeutic agents in the treatment of this disease.
Section snippets
Protein kinase CK2: a master regulator of cell survival
Protein kinase CK2 is composed by the assembly of 2 catalytic α and 2 regulatory β subunits, forming a tetramer α2β2. The alternative α′ catalytic subunit, encoded by a distinct gene, may also take part in the generation of tetramers either α′2β2 or α′αβ2. CK2 is a pleiotropic PK that has been demonstrated to be involved in a multitude of different cellular processes [14]. Nevertheless, despite its multitasking function in the cell, it has been possible to describe a prevalent role for this
Protein kinase CK2 in MM cell growth: role in the regulation of the NF-κB and STAT3 signaling pathways
MM cells depend for their growth and survival on signals arising from intrinsic and extrinsic over-activated signaling pathways. In other cell types, a number of myeloma-regulating signaling cascades have been described to be variably influenced by the activity of PK CK2. Our laboratory was thus involved in studies aimed at answering the question of whether CK2 could take part in the pathogenesis of MM. We assumed that this kinase could regulate signals originating from growth factors as well
Protein kinase CK2 in MM cell growth: role in the regulation of the Hsp90 and the endoplasmic reticulum (ER) stress/unfolded protein response pathways
A subsequent paper from our group demonstrated that CK2 might impinge on the response of MM plasma cells to unfolded protein (UPR) and endoplasmic reticulum stress. This homeostatic process has recently been implicated in the development, survival and malignant growth of B-lymphocytes and plasma cells [5], [19], [20], [21]. In this work, it has been shown that CK2 localizes not only in the cytoplasm but also in the ER of normal and malignant plasma cells and that the triggering of ER-stress
GSK3: from the involvement in a “sweet” pathway to a bitter role in cancer growth
Two distinct genes, GSK3α and GSK3β, which share homology in most of the protein domains, encode GSK3. GSK3α and GSK3β might have common as well as different functions in the cell [27].
GSK3 was initially recognized as a regulative kinase of the insulin-glucose pathway. GSK3 phosphorylation of glycogen kinase and of initiation factor eIF2B causes inhibition of glycogen and protein synthesis. Upon insulin stimulation, AKT1 activation causes GSK3 phosphorylation on Ser9 (GSK3β) and Ser21 (GSK3α)
GSK3: pro-growth role in MM
A number of studies have investigated the expression and function of GSK3 in MM cells and the data so far available must be considered early; nevertheless, they contributed important insights to prompt a more detailed analysis of this kinase.
Initial reports showed that GKS3 inhibitors were able to cause apoptosis of MM cell lines, causing dephosphorylation of forkhead transcription factors FKHRL1and FKHR and activation of the cyclin dependent kinase p27kip1 [32], [33].
Another study analyzed in
GSK3 in MM-associated bone disease
The role of GSK3 could be, however, even more complex. Indeed, the function of this kinase in bone developmental processes can be exploited to modulate multiple myeloma-associated bone alterations: the action of GSK3 on the Wnt/β-catenin pathway can profoundly impact on the maturation of the osteoblasts and osteogenesis. In MM this latter process is impaired by modifications induced in the BM milieu, and, among others, by the increased secretion of soluble Wnt inhibitors, such as Dickkopf-1
Conclusions
The pathogenesis of MM is complex and driven by alterations occurring in malignant plasma cells as well as in the MM microenvironment. Novel therapeutic approaches are designed to exert anti-myeloma effects by acting on these two levels. The search for molecular regulators of MM growth and survival is continuously progressing. Protein kinases are central in the promotion of MM cell growth [1]. The serine threonine kinases that we have herein discussed are two novel recently identified
Conflict of interest
The Authors declare that no conflict of interest are present.
Acknowledgements
This work was supported by grants from Italian Ministry of University (FIRB “Futuro in Ricerca” – RBFR086EW9_001) and from University of Padova (“Progetti di Ricerca di Ateneo” – CPDA114940/11) to F.P. and from a grant from Associazione Italiana per la Ricerca sul Cancro (AIRC) to G.S.
References (44)
- et al.
Multiple myeloma
Lancet
(2009) - et al.
New drugs in multiple myeloma: mechanisms of action and phase I/II clinical findings
Lancet Oncol
(2008 Dec) - et al.
Emerging treatments for multiple myeloma: beyond immunomodulatory drugs and bortezomib
Semin Hematol
(2009) - et al.
The genetic architecture of multiple myeloma
Nat Rev Cancer
(2012) - et al.
Pathogenesis of myeloma
Annu Rev Pathol
(2011) - et al.
Many multiple myelomas: making more of the molecular mayhem
Hematology/Am Soc Hematol Educ Program
(2011) - et al.
Novel therapies in MM: from the aspect of preclinical studies
Int J Hematol
(2011) - et al.
Addiction to protein kinase CK2: a common denominator of diverse cancer cells?
Biochim Biophys Acta
(2010) - et al.
Glycogen synthase kinase-3 in insulin and Wnt signalling: a double-edged sword?
Biochem Soc Trans
(2004) - et al.
Shaping the nuclear action of NF-kappaB
Nat Rev Mol Cell Biol
(2004)
Functional interaction of protein kinase CK2 and c-Myc in lymphomagenesis
Oncogene
GSK3 regulates the expressions of human and mouse c-Myb via different mechanisms
Cell Div
Serine-threonine protein kinases CK1, CK2 and GSK3 in normal and malignant haematopoiesis
Curr Signal Transd Ther
Protein kinase CK2 in health and disease: CK2: a key player in cancer biology
Cell Mol Life Sci
Protein kinase CK2, a key suppressor of apoptosis
Adv Enzyme Regul
Addiction to protein kinase CK2: a common denominator of diverse cancer cells?
Biochim Biophys Acta
Protein kinase CK2 in hematologic malignancies: reliance on a pivotal cell survival regulator by oncogenic signaling pathways
Leukemia
Multiple myeloma cell survival relies on high activity of protein kinase CK2
Blood
Heat shock protein inhibition is associated with activation of the unfolded protein response pathway in myeloma plasma cells
Blood
Regulation of basal cellular physiology by the homeostatic unfolded protein response
J Cell Biol
Identification of an Ire1alpha endonuclease specific inhibitor with cytotoxic activity against human multiple myeloma
Blood
CK2 controls multiple protein kinases by phosphorylating a kinase-targeting molecular chaperone, Cdc37
Mol Cell Biol
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