Abstract
ABSTRACT The specificity, stability and reversibility of the in vitro interaction of LATS with soluble human thyroid fractions was studied. With regard to tissue specificity, the cell sap obtained from human liver, spleen, kidney, and muscle did not inhibit the LATS activity while the same amount of thyroid cell sap significantly inhibited it. When the LATS inhibitory activity in thyroid subcellular fractions was compared, the microsomal fraction was more active than cell sap or solubilized microsomes in terms of milligram of protein, but the cell sap had considerable activity as based on the original thyroid weight. Lyophilization of cell sap did not reduce the LATS inhibitory activity, but treatment with 2 m NaSCN and 6 m urea apparently destroyed this capacity. Acid treatment of cell sap at pH 2.5 and at 3.0 completely destroyed its ability to inhibit LATS activity. Inhibition of LATS activity was roughly proportional to the amount of thyroid cell sap. Human TSH, on the other hand, was not inhibited by cell sap which had a significant inhibitory effect on LATS. LATS activity was more effectively inhibited when a mixture of LATS-IgG and thyroid cell sap was incubated for 96 hours than for 12 hours. The inhibition of LATS activity by thyroid cell sap was partially but significantly reversed by acid treatment, as observed in experiment using microsomes. When thyroid cell sap was fractionated by gel filtration on Sepharose 4B, LATS inhibitory activity was distributed in all the fractions including the 27S to 4S proteins. In DEAE-cellulose column chromatography, LATS inhibitory activity tended to be eluted at a higher ionic strength. In each fraction of Sepharose 4B and DEAE-cellulose, LATS inhibitory activity was found to be unrelated to the thyroglobulin content. It is believed that the inhibition of LATS activity by thyroid cell sap is compatible with an antigen-antibody reaction and that the LATS inhibitor may not be a thyroglobulin itself but a more negatively charged heterogeneous substance.
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