Protein kinase WNK2 inhibits cell proliferation by negatively modulating the activation of MEK1/ERK1/2.

The recently identified subfamily of WNK protein kinases is characterized by a unique sequence variation in the catalytic domain and four related human WNK genes were identified. Here, we describe the cloning and functional analysis of the human family member WNK2. We show that the depletion of endogenous WNK2 expression by RNA interference in human cervical HeLa cancer cells led to the activation of the extracellular signal-regulated kinase (ERK)1/2 mitogen-activated protein kinases but, in contrast to the depletion of WNK1, had no effect on ERK5. Furthermore, expression of a kinase-dead WNK2-K207M mutant also activated ERK1/2 suggesting that WNK2 catalytic activity is required. Depletion of WNK2 expression increased G1/S progression and potentiated the cellular response to low epidermal growth factor concentrations. The molecular mechanism of ERK1/2 activation in WNK2-depleted cells lies downstream of the Raf kinases and involves MEK1 phosphorylation at serine 298 in both HeLa and HT29 colon cancer cells. This modification is linked to the upregulation of MEK1 activity toward ERK1/2. Together, these results provide evidence that WNK2 is involved in the modulation of growth factor-induced cancer cell proliferation through the MEK1/ERK1/2 pathway. The data identify WNK2 as a candidate tumor suppressor gene and suggest a coordinated activity of WNK kinases in the regulation of cell proliferation.

Medullary carcinomas of the thyroid: a monoclonal origin.

We studied the clonality of medullary thyroid carcinomas (MTC) from 16 female patients by determining X chromosome inactivation by polymerase chain reaction (PCR) amplification of a CAG repeat in exon 1 of the human androgen-receptor gene. One patient with sporadic medullary thyroid carcinoma (MTC) was homozygous for this microsatellite and was not considered for the assessment of clonality. Sixteen tumor samples from the informative 15 patients were studied: 11 were from sporadic cases and 5 were from familial cases (3 cases of multiple endocrine neoplasia type 2A [MEN 2A]; 1 case of familial medullary thyroid carcinoma [FMTC]). Fourteen tumor samples (10/11 sporadic, 3/4 MEN 2A and 1/1 FMTC) were clearly monoclonal with allelic cleavage ratios between 2.5 and 49.1. Sixty-four percent of these cases (9/14) had the preferential amplification of the shorter allele while 36 percent (5/14) had the preferential amplification of the longer allele. Two frozen tumor samples (1 sporadic and 1 MEN 2A) were polyclonal. However, the corresponding tumor embedded in paraffin from the sporadic case was monoclonal. The other polyclonal tumor was found in the right thyroid lobe of a patient with MEN 2A who had a monoclonal tumor in the left lobe. Our results clearly demonstrate that MTC have a monoclonal origin in the majority of the cases.