A kinase/phosphatase system involving the protooncogene Lck is necessary for inducible modulation of Sob 1 during T cell activation

The phosphotyrosine containing protein Sob 1 regulates inducibility of a DNA binding complex (Band A) at the SRE of c-fos during T cell activation. In the present study, Sob 1 was regulated by activation of T cells through the T cell antigen receptor. Inhibition of protein tyrosine kinases (PTK) inactivated Sob 1 function and allowed the Band A DNA-protein complex to form. Inhibition of protein tyrosine phosphatases (PTP) caused constitutive activation of Sob 1 function and prevented induction of Band A at the SRE. Thus, Sob 1 is regulated by a constitutive PTP/PTK system. J.CaM 1 cells that lack a functional form of the PTK Lck are unable to induce Band A through the T cell antigen receptor. J.CaM 1 cells reconstituted with Lck seem to induce Band A normally. Thus, functional Lck is required for regulation of Sob 1.

Modulation of T cell morphology and induction of homotypic adhesion by a protein tyrosine kinase inhibitor

T cells are spherical in culture and during travel through the bloodstream. They depart from this shape as part of the adhesion cascade by which they penetrate endothelium, interact with the extracellular matrix, and migrate through tissues. The mechanisms by which shape changes and altered adhesive properties are regulated are largely uncharacterized; however, they involve modulation of protein phosphorylation on tyrosine. Here, an inhibitor (MDHC) of protein tyrosine kinases (PTK) caused a shift in the morphology of a human T cell line from spherical to spread. This involved cytoskeletal components and was preceded by altered tyrosyl-phosphorylation and accompanied by an increased capacity for homotypic adhesion involving LFA-1 and CD2. Examples exist demonstrating prevention of morphological alteration or cell adhesion by PTK inhibitors, and thus MDHC differed from these other inhibitors. This suggests differential sites of action for PTK inhibitors and perhaps that MDHC accessed different steps in the adhesion cascade.

Amplification of the Bacillus subtilis maf gene results in arrested septum formation

The Bacillus subtilis homolog of the Escherichia coli morphogene orfE (of the mre operon) has been identified. The determinant is located on the chromosome immediately upstream of the mreBCD-minCD (divIVB) operon. The Maf protein shares substantial amino acid sequence identity with the E. coli OrfE protein. Introduction of the B. subtilis maf determinant on a multicopy plasmid into B. subtilis cells results in an inhibition of septation, which leads to extensive filamentation and loss of viability in the transformed cell population. Insertional inactivation of maf indicated that this gene is not essential for cell division.