H4(D10S170), a gene frequently rearranged with RET in papillary thyroid carcinomas: functional characterization.

Human thyroid papillary carcinomas are characterized by rearrangements of the RET protooncogene with a number of heterologous genes, which generate the RET/papillary thyroidcarcinoma(PTC)oncogenes.Oneofthemost frequent variants of these recombination events is the fusion of the intracellular kinase-encoding domain of RET to the first 101 amino acids of a gene named H4(D10S170).WehavecharacterizedtheH4(D10S170) gene product, showing that it is a ubiquitously expressed 55KDa nuclear and cytosolic protein that is phosphory- latedfollowingserumstimulation.Thisphosphorylation was found to depend on mitogen-activated protein kinase(MAPK)Erk1/2activityandtobeassociated totherelocationofH4(D10S170)fromthenucleusto the cytosol. Overexpression of the H4(D10S170) gene was able to induce apoptosis of thyroid follicular epithelial cells; conversely a carboxy-terminal truncated H4(D10S170) mutant H4(1-101), corresponding to the portion included in the RET/PTC1 oncoprotein, behaved as dominant negative on the proapoptotic function and nuclear localization of H4(D10S170). Furthermore, con- ditional expression of the H4(D10S170)-dominant nega- tive truncated mutant protected cells from stress-induced apoptosis. The substitution of serine 244 with alanine abrogated the apoptotic function of H4(D10S170). These data suggest that loss of the H4(D10S170) gene function might have a role in thyroid carcinogenesis by impairing apoptosis.