Alterations in expression of p56lck during myeloid differentiation of LSTRA cells

The src-related tyrosine kinase p56lck is overexpressed in the mouse leukemia cell line LSTRA. Although p56lck is thought to be a specific T-cell marker, we found that LSTRA cells can be induced to differentiate towards macrophages or granulocytes by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate or the cyclic nucleotide analogue, dibutyryl cAMP, respectively. Treatment of LSTRA cells with 12-O-tetradecanoylphorbol-13-acetate resulted in marked alterations in morphology including increased size, adherence, and spreading on culture dishes. These cells also ceased proliferating, accumulated in G0-G1 and expressed nonspecific esterase activity. In contrast, although LSTRA cells treated with dibutyryl cAMP stopped growing and accumulated in G0-G1, these cells expressed functionally active chemotactic peptide receptors and became irregular and granular in appearance. Differentiation of LSTRA cells was also found to be associated with altered expression of p56lck. Thus, while 12-O-tetradecanoylphorbol-13-acetate treatment caused the cells to produce higher molecular weight forms of p56lck, dibutyryl cAMP treatment resulted in increased expression of total p56lck mRNA as well as the more mature type II p56lck mRNA transcript. There were no major alterations in p56lck kinase activity in vitro following differentiation. Phospholipase C gamma and p21rasGAP, two putative substrates for the tyrosine kinase activity of p56lck, were found to be constitutively phosphorylated on tyrosine in LSTRA cells. Tyrosine phosphorylation of these substrates was not altered following differentiation. These results indicate that LSTRA cells are relatively early precursors that have the capacity to develop along the myeloid differentiation pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular depletion of p56lck during thymocyte apoptosis

The src-related protein tyrosine kinase p56lck is thought to be important in regulating maturation and functional responsiveness of T cells and thymocytes. In the present studies we report that expression of p56lck is suppressed during apoptosis. Using primary cultures of rat thymocytes, we found that agents that are effective in inducing apoptosis, including okadaic acid, dexamethasone, and antibodies to the CD3 receptor, also deplete cells of p56lck. This process is rapid, occurring within 24 h, and is not due to cytotoxicity. Inhibition of DNA fragmentation in apoptotic cells with the endonuclease inhibitor ZnCl2 failed to prevent depletion of p56lck, suggesting that it was not a consequence of the DNA degradation process. Using the thymic lymphoma cell line LSTRA, apoptosis was also associated with cellular depletion of p56lck. In contrast to thymocytes, this process required 48-72 h possibly because these cells overexpress p56lck. Although at this time we are uncertain as to the precise role of p56lck in the process of apoptosis, our results indicate that changes in the expression of this protein in thymocytes is an important marker of programmed cell death.

Production of nitric oxide by differentiated LSTRA cells is associated with expression of macrophage-inducible nitric oxide synthase

LSTRA is a mouse lymphoma cell line overexpressing the src-related oncogene product and T cell marker p56lck. We have discovered that LSTRA cells, like HL60 and U937 promyelocytic leukemia cells, can be induced to differentiate toward macrophages by the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) or granulocytes by the cyclic nucleotide analogue dibutyryl cAMP (dbcAMP). One property of mature macrophages and granulocytes is the ability to produce nitric oxide, a highly reactive free radical that is important in non-specific host defense. Nitric oxide production by mature macrophages is stimulated by inflammatory mediators via an inducible form of the enzyme, nitric oxide synthase. We report that LSTRA cells acquire the ability to produce nitric oxide following differentiation induced by TPA and, to a lesser extent, by dbcAMP. Nitric oxide production by the cells is dependent on L-arginine and blocked by several inhibitors of nitric oxide synthase, including N-monomethyl-L-arginine, L-canavanine, L-arginine benzyl ester, and L-arginine methyl ester. In macrophage-differentiated LSTRA cells, the inflammatory cytokine interferon-gamma was found to be a potent inducer of nitric oxide production. This was correlated with a marked increase in nitric oxide synthase activity in the cells that was due to interferon-gamma-induced expression of the macrophage-inducible form of nitric oxide synthase protein as well as mRNA. Differentiated LSTRA cells also expressed increased amounts of a constitutive form of nitric oxide synthase that was also present in undifferentiated cells. Taken together with previous findings, these results support the model that LSTRA cells have the capacity to differentiate toward mature macrophages.

Interleukin-1 stimulates glucose transport in rat adipose cells. Evidence for receptor discrimination between IL-1 beta and IL-1 alpha

The effect of interleukin 1 (IL-1) on glucose transport activity in isolated rat adipose cells was examined. IL-1 beta stimulated 3-O-methylglucose (3OMG) transport in a time and dose dependent manner. This effect appears to be due to increased maximal transport velocity (Vmax) of the carrier. Addition of insulin and IL-1 beta resulted in an additive stimulation of transport, suggesting different mechanisms. IL-1 alpha had no effect on glucose transport. Glu-4, a relatively inactive IL-1 beta analogue in most cells, stimulated glucose uptake in a time and dose dependent manner with kinetics indistinguishable from those of IL-1 beta.