Protein kinase Akt activity in human thyroid tumors

We studied the expression and activation of the main effector protein kinase of phosphatidylinositol-3-kinase cascade (PI3K) – Akt in conventionally normal tissues, benign and highly differentiated (with and without metastases) human thyroid tumors. There was a difference in the Akt1 amount in tumor tissue compared with normal tissue in papillary carcinomas and tissue of multinodular goiter. Akt expression both in tumor and conventionally normal tissues of follicular adenoma was significantly lower than in follicular carcinoma. The lowest level of Akt expression was observed in tissues of multinodular goiter. Total activity of all three isoforms of Akt1/2/3 was lower in tumors compared to conventionally normal tissue. Thus, Akt activity (according to Thr308 phosphorylation) is not associated with proliferative processes in the tumor tissue of the thyroid. Apoptosis level detected in these tissues was not associated with the protein kinase activity either. Possible mechanisms of signaling cascade PI3K/Akt inhibition in thyroid tumors are discussed.