Cdk5 Regulates STAT3 Activation and Cell Proliferation in Medullary Thyroid Carcinoma Cells

Abstract

The biological behaviors of thyroid cancer are varied, and the pathological mechanisms remain unclear. Some reports indicated an apparent aggregation of amyloid accompanying medullary thyroid carcinoma (MTC). Amyloid aggregation in neurodegeneration leads to hyperactivation of Cdk5 and subsequent neuronal death. Based on the connection with amyloid, the role of Cdk5 in MTC is worthy of investigation. Initially, the expression of Cdk5 and its activator, p35, in MTC cell lines was identified. Cdk5 inhibition by specific inhibitors or short interfering RNA decreased the proliferation of MTC cell lines, which reveals the importance of Cdk5 in MTC cell growth. Although p35 cleavage has been considered as an important element in neurodegeneration, it seems that p35 cleavage was not a major cause in Cdk5 activity-dependent MTC cell proliferation because neither Cdk5 activity nor cell growth was affected by the inhibition of p35 cleavage. Clearance of amyloid by antibody neutralization indicated that MTC cell proliferation was supported by calcitonin-derived extracellular amyloid and subsequent Her2 and Cdk5 activation. Significantly, the STAT3 pathway was involved in Cdk5-dependent proliferation of MTC cells through Ser-727 phosphorylation. In addition, Cdk5 inhibition reduced nuclear distributions of both the Cdk5-p35 complex and phospho-STAT3 in MTC cells. Finally, Cdk5 inhibition retarded tumor formation in vivo accompanying the reduction of phospho-STAT3. Our findings suggest the first demonstration of a novel and specific role for Cdk5 kinase in supporting the proliferation of the medullary thyroid carcinoma cells and could shed light on a new field for diagnosis and therapy of thyroid cancer. Medullary thyroid carcinoma (MTC)2 is transformed from parafollicular C cells, which are primarily responsible for secretion of calcitonin in the thyroid gland. An abnormal increase of blood calcitonin is a common symptom for MTC (1, 2), a type of carcinoma that may be associated with MEN2 (multiple endocrine neoplasia-type 2). MEN2 occurs along with pheochromocytomas or adrenal medullary hyperplasia, in which many endocrine glands such as the thyroid, adrenals, and parathyroid are affected simultaneously in a patient. MTC has been demonstrated to be associated with amyloid fibrils aggregated in the thyroid and adjacent tissues (3). Amyloid is a self-aggregated polypeptide and tends to form insoluble fibrils that are extracellularly deposited in many protein-folding disorders such as Alzheimer disease (AD) and other amyloidoses because of overexpression, proteolytic digestion, or mutations of its precursor protein (4). In addition to typical amyloid-related diseases, type II diabetes, myocardial infarctions, and several kinds of cancers were found to be associated with amyloid aggregation. In these cases, non-neoplastic and malignant tumors of the breast, lung squamous cell carcinoma, and MTC are all associated with amyloid (5).Cdk5 (cyclin-dependent kinase 5) is a member of a small serine/threonine cyclin-dependent kinase f...

RNAi screen of the druggable genome identifies modulators of proteasome inhibitor sensitivity in myeloma including CDK5

“…33 CDK5 was also previously shown to enhance tumor cell proliferation and invasion. [28][29][30]34 CDK5's targets include several important proteins for cell growth and death, such as STAT3, AKT, BCL-2, p53, and RB. 29,[34][35][36][37] By testing multiple CDK5 siRNAs and shRNAs, we confirmed that CDK5 knockdown sensitizes genetically variable myeloma cell lines to bortezomib and other proteasome inhibitors.…”

“…[28][29][30]34 CDK5's targets include several important proteins for cell growth and death, such as STAT3, AKT, BCL-2, p53, and RB. 29,[34][35][36][37] By testing multiple CDK5 siRNAs and shRNAs, we confirmed that CDK5 knockdown sensitizes genetically variable myeloma cell lines to bortezomib and other proteasome inhibitors. This finding and its clinical relevance were further explored by the use of CDK5 inhibitors, roscovitine and SCH727965, which were demonstrated to synergize with bortezomib to induce cytotoxicity of both MM cell lines and primary MM samples.…”

“…25 Although activity of CDK5 is most evident in neuronal tissues, CDK5 is also active in some non-neuronal tissues 26,27 and survival and metastasis of several tumor cells, including breast, prostate, thyroid, and colon cancer cells. 11,[28][29][30] Upregulation of CDK5 was recently identified as one of genetic changes related to oxaliplatin resistance acquisition in colorectal cancer cells. 31 A recent RNAi screening study demonstrated that silencing CDK5 enhanced the sensitivity to a PARP inhibitor in a breast cancer cell line.…”

Cyclin-dependent kinase 5 regulates the proliferation, motility and invasiveness of lung cancer cells through its effects on cytoskeletal remodeling

“…Compared with other CDKs, CDK5 is considered to be an essential regulator of neuronal differentiation, rather than a cell cycle regulator; and controls a wide range of functions, including synapse formation, neuronal migration and axon guidance (7), all of which indicate that CDK5 is important as a 'migration mediator'. Notably, CDK5 had been found to be correlated with increased invasion in prostate carcinoma, glioblastoma multiforme (8,9), pancreatic cancer cells (10,11) and medullary thyroid cancer (12). The inhibition of the activity of CDK5 decreases cancer cell migration and invasion (13), however, the mechanism underlying the involvement of CDK5 in tumorigenesis remains to be fully elucidated.…”

Single-nucleotide polymorphisms in the promoter of the CDK5 gene and lung cancer risk in a Korean population

“…There is presently a substantial amount of data to indicate that CDK5 plays important roles in extraneuronal cells during the process of myogenesis, lens differentiation, spermatogenesis, insulin secretion, apoptosis of ovarian cells and hematopoietic cell differentiation. 3,[5][6][7][8][9][10][11] Furthermore, CDK5 has been suggested to play roles in the regulation of motility of prostate cancer cells, 12 control of glioblastoma cell invasion, 13 modulation of proliferation of medullary thyroid carcinoma cells 14 and apoptotic control of leukemia cells. 15 These potential roles of CDK5 activity in the carcinogenesis of each cell type seem to involve distinct target substrates.…”