TPA Treatment Of Cells Research Articles

Proteolytic Cleavage of the CD44 Adhesion Molecule in Multiple Human Tumors

Cell surface adhesion molecules are crucial for the development and/or pathogenesis of various diseases including cancer. CD44 has received much interest as a major adhesion molecule that is involved in tumor progression. We have previously demonstrated that the ectodomain of CD44 undergoes proteolytic cleavage by membrane-associated metalloproteases in various tumor cell lines. The remaining membrane-bound CD44 cleavage product can be detected using antibodies against the cytoplasmic domain of CD44 (anti-CD44cyto antibody). However, the cleavage of CD44 in primary human tumors has not been investigated. Using Western blots with anti-CD44cyto antibody to assay human tumor tissues, we show that the CD44 cleavage product can be detected in 58% (42 of 72) of gliomas but not in normal brain. Enhanced CD44 cleavage was also found in 67% (28 of 42) of breast carcinomas, 45% (5 of 11) of non-small cell lung carcinomas, 90% (9 of 10) of colon carcinomas, and 25% (3 of 12) of ovarian carcinomas. Tumors expressing a CD44 splice variant showed a significantly higher incidence of enhanced CD44 cleavage. The wide prevalence of CD44 cleavage suggests that it plays an important role in the pathogenesis of human tumors.

C-Myc transactivation domain-associated kinases: questionable role for map kinases in c-Myc phosphorylation.

We have isolated and characterized cellular kinases which associate with the transactivation domain of c-Myc and phosphorylate Ser-62. We demonstrate that cellular Map kinases associate with c-Myc under stringent conditions and phosphorylate Ser-62. We also find that TPA stimulates the activity of the Myc-associated Map kinase to phosphorylate Ser-62. However, we do not observe an increase in Ser-62 phosphorylation in endogenous c-Myc after TPA treatment of cells. Since the regulation of the c-Myc-associated Map kinases does not correlate with the in vivo regulation of Ser-62 phosphorylation in c-Myc, we conclude that Map kinases are not the in vivo kinases for Ser-62. Although Ser-62 phosphorylation was not affected by TPA, phosphorylation at a different serine residue was significantly upregulated by TPA.

Expression and Phosphorylation of Transferrin Receptors in Mitogen-Activated Peripheral Blood Lymphocytes1

Expression of transferrin receptors of cultured human lymphocytes has been investigated by using monoclonal antibody (5E9) specific for human transferrin receptors. When isolated lymphocytes were cultured in a medium containing fetal calf serum, the biosynthesis of transferrin receptor was barely detectable. The addition of concanavalin A or human serum to the medium caused a slight stimulation of the biosynthesis. The addition of concanavalin A and human serum in combination caused the highest biosynthetic activity. Appearance of the receptor on the cell surface increased in parallel with the degree of the synthesis. Treatment of concanavalin A- and human serum-treated cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) resulted in a marked stimulation of the phosphorylation of the receptor. Enhancement of phosphorylation occurred within 20 min after the addition of TPA. The density of the receptor on the cell surface slightly increased upon TPA treatment of cells, and the treatment was without effect on iron incorporation from transferrin into the cells. The density of newly synthesized receptor in TPA-treated cells was similar to that in non-treated cells. These results indicated that TPA treatment of mitogen-activated human lymphocytes stimulated the phosphorylation of transferrin receptors, but TPA had no effect on the expression of the receptors thereafter.

Differentiation of human leukemias in response to 12-0- tetradecanoylphorbol-13-acetate in vitro

Leukemic cells from patients with acute myeloid leukemia underwent morphological, functional, and histochemical changes within 24–48 hr after treatment with 1.6 x 10–18 M 12–0-tetradecanoylphorbol-13-acetate (TPA). The changes included adhesion to the plastic substrate, a 4–6- fold increase in the number of phagocytic cells, and an increase in the number of alpha-naphthyl-acetate esterase (alpha-NAE) positive cells. In contrast, TPA treatment of cells from patients with acute lymphoblastic leukemia caused some aggregation of cells in suspension, but no changes in adhesion, phagocytosis, or alpha-NAE. Of the four cases of undifferentiated or unclassified leukemias studied, two failed to respond to TPA, one responded with a myeloid (adhesion) pattern, and one with a lymphoid (aggregation) pattern. These data suggest that leukemic myeloblasts retain the ability to express a variety of differentiated functions, and in some cases, it may be possible to use TPA as a tool to test the differentiative potential of undifferentiated human leukemias.

Differentiation of human leukemias in response to 12-0- tetradecanoylphorbol-13-acetate in vitro

Leukemic cells from patients with acute myeloid leukemia underwent morphological, functional, and histochemical changes within 24-48 hr after treatment with 1.6 × 10-18M 12-0-tetradecanoylphorbol-13-acetate (TPA). The changes included adhesion to the plastic substrate, a 4-6-fold increase in the number of phagocytic cells, and an increase in the number of alpha-naphthyl-acetate esterase (α-NAE) positive cells. In contrast, TPA treatment of cells from patients with acute lymphoblastic leukemia caused some aggregation of cells in suspension, but no changes in adhesion, phagocytosis, or α-NAE. Of the four cases of undifferentiated or unclassified leukemias studied, two failed to respond to TPA, one responded with a myeloid (adhesion) pattern, and one with a lymphoid (aggregation) pattern. These data suggest that leukemic myeloblasts retain the ability to express a variety of differentiated functions, and in some cases, it may be possible to use TPA as a tool to test the differentiative potential of undifferentiated human leukemias.