3,5,3'-Tri-iodo-L-thyronine acutely regulates a protein kinase C-sensitive, Ca2+-independent, branch of the hepatic alpha1-adrenoreceptor signalling pathway

Short-term effects of thyroid hormones on Na+-K+-ATPase activity of chick embryo hepatocytes during development: focus on signal transduction

Nongenomic effects of thyroid hormones on Na+-K+-ATPase activity were studied in chick embryo hepatocytes at two different developmental stages, 14 and 19 days of embryonal age, and the signal transduction pathways involved were characterized. Our data showed the following. 1) 3,5,3′-Triiodo-l-thyronine (T3) and 3,5-diiodo-l-thyronine (3,5-T2) rapidly induced a transient inhibitory effect on the Na+-K+-ATPase; the extent and duration depended on the developmental age of the cells. 2) 3,5-T2behaved as a true hormone and fully mimicked the effect of T3. 3) Thyroxine had no effect at any of the developmental stages. 4) The inhibition of Na+-K+-ATPase was mediated by activation of protein kinase A, protein kinase C, and phosphoinositide 3-kinase, suggesting several modes of modulation of ATPase activity through phosphorylation at different sites. 5) The MAPK pathway did not seem to be involved in the early phase of hormone treatment. 6) The nonpermeant analog T3-agarose inhibited Na+-K+-ATPase activity in the same way as T3, confirming that hormone signaling initiated at a receptor on the plasma membrane. From these results, it can be concluded that the cell response mechanisms change rapidly and drastically within the early phase of embryo growth. The differences found at the two stages probably reflect the different roles of thyroid hormones during development and differentiation.

Lymphosarcoma-induced alterations in hepatic adrenergic receptors: implications to the hypoglycemia of cancer cachexia

A highly malignant transplantable rat lymphosarcoma was studied to determine the involvement of hepatic adrenergic receptors in the development of the hypoglycemia of cancer cachexia. Following inoculation of Fischer 344 rats with lymphosarcoma cells, rats were examined at 2 and 4 weeks, at the pre-cachexic stage; 6 weeks, at the transitional stage; and 7 weeks, at the cachexic hypoglycemic stage of lymphosarcoma progression. Death occurred by the 8th week. Blood glucose levels in lymphosarcoma-bearing rats relative to control rats were: unaffected at week 2; significantly reduced 8% at weeks 4 and 6; and reduced 24% at week 7. Alpha1 adrenergic receptor binding to plasma membranes isolated from the livers of lymphosarcoma-bearing rats was: 114, 89, 67 and 30% of control at weeks 2, 4, 6, and 7, respectively. Kinetic analysis indicated that the lymphosarcoma-induced decrease at week 7 was due to a decrease in numbers of receptors with no change in affinity: B(max)(control): 1411.1 fmol/mg: Kd(control): 0.44 nm; B(max)(lympho): 345.5 fmol/mg; Kd(lympho): 0.50 nm. Alpha2 adrenergic receptor binding to plasma membranes isolated from the livers of lymphosarcoma-bearing rats was: 130, 137, 243 and 212% of control at weeks 2,4, 6, and 7, respectively. The pattern of changes in hepatic alpha1, alpha2 and beta adrenergic receptors at week 6 was comparable to that of 17 day fetal liver: a decrease in alpha1 and beta and an increase in alpha2. Hepatic adrenergic receptor changes occurred in the absence of liver damage and were not due to contamination of the liver plasma membrane fractions with lymphosarcoma cells. Plasma insulin levels displayed modest (10-15%), but not statistically significant, increases post-inoculation after week 4. Plasma glucagon levels fluctuated post-inoculation until week 7 where they were significantly increased: 202% of control. Plasma T3 and T4 levels displayed an early and steady decline after lymphosarcoma inoculation: T3: unchanged at week 2 and significantly decreased 14, 44 and 50% at weeks 4, 6 and 7, respectively. T4 increased 20% at week 1; decreased 9% at week 4 and significantly decreased thereafter: 55 and 49% at weeks 6 and 7, respectively. We propose that the development of the hypoglycemia of cancer cachexia in this lymphosarcoma model is due primarily to an early and progressive thyroid hormone dependent decrease in the number of hepatic alpha1 adrenergic receptors, compounded by an increase and decrease, respectively, in the hepatic beta and alpha2 adrenergic receptors.

Activation of mitogen-activated protein kinases is required for alpha1-adrenergic agonist-induced cell scattering in transfected HepG2 cells

Activation of alpha1B-adrenergic receptors ((alpha1B)AR) by phenylephrine (PE) induces scattering of HepG2 cells stably transfected with the (alpha1B)AR (TFG2 cells). Scattering was also observed after stimulation of TFG2 cells with phorbol myristate acetate (PMA) but not with hepatocyte growth factor/scatter factor, epidermal growth factor, or insulin. PMA but not phenylephrine rapidly activated PKCalpha in TFG2 cells, and the highly selective PKC inhibitor bisindolylmaleimide (GFX) completely abolished PMA-induced but not PE-induced scattering. PE rapidly activated p44/42 mitogen-activated protein kinase (MAPK), p38 MAPK, c-Jun N-terminal kinase (JNK), and AP1 (c-fos/c-jun). Selective blockade of p42/44 MAPK activity by PD98059 or by transfection of a MEK1 dominant negative adenovirus significantly inhibited the PE-induced scattering of TFG2 cells. Selective inhibition of p38 MAPK by SB203850 or SB202190 also blocked PE-induced scattering, whereas treatment of TFG2 cells with the PI3 kinase inhibitors LY294002 or wortmannin did not inhibit PE-induced scattering. Blocking JNK activation with a dominant negative mutant of JNK or blocking AP1 activation with a dominant negative mutant of c-jun (TAM67) significantly inhibited PE-induced cell scattering. These data indicate that PE-induced scattering of TFG2 cells is mediated by complex mechanisms, including activation of p42/44 MAPK, p38 MAPK, and JNK. Cell spreading has been reported to play important roles in wound repair, tumor invasion, and metastasis. Therefore, catecholamines acting via the (alpha1)AR may modulate these physiological and pathological processes.