Epidermal growth factor, polyamines, and epithelial remodeling in Caco-2 cells

Expression of spermidine/spermine N1-acetyltransferase in HeLa cells is regulated by amino acid sufficiency

The effect of amino acids on the regulation of the expression of spermidine/spermine N(1)-acetyltransferase (SSAT), the key enzyme of polyamine catabolism, was studied in HeLa cells. When compared with similar exposure to complete medium, deprivation of arginine, methionine or leucine gave rise to a time-dependent, slowly reversible increase in the cellular level of SSAT mRNA that started to be significant after 8, 12 or 16h and reached four-, five- and two-fold after 16h, respectively. Experiments utilizing (i) constructs containing fragments of the SSAT promoter linked to a luciferase reporter gene or (ii) actinomycin D (Act-D)-treated cells indicated that the increase in the SSAT mRNA level was due to an augmentation in gene transcription and message stability after omission of one of the polyamine precursor amino acids. By contrast, SSAT mRNA stabilisation was only observed when leucine was the omitted amino acid. Amino acid deprivation was also found to cause increased intracellular activity of SSAT concurrent with changes in the cell polyamine content, namely increased putrescine but decreased spermine levels. Furthermore, stable expression of a dominant negative mutant of stress-activated protein kinase/extracellular signal-regulated protein kinase (SAPK/ERK) kinase 1 in HeLa cells was found to inhibit the increase in SSAT mRNA by amino acid deprivation. The data suggest that c-Jun N-terminal kinase/SAPK (JNK/SAPK) may be involved in the amino acid-dependent regulation of SSAT expression.

Endomorphin-1 alters interleukin-8 secretion in Caco-2 cells via a receptor mediated process

Administration of opioids that bind to the classical mu opioid receptor has been shown to lead to unintended alterations in immune function. Traditionally, altered immune function has been investigated with circulating immune cells. Effects of mu agonists on intestinal epithelial immune function have not been described. Since the oral route of administration is frequently employed with opiates, we determined if the mu receptor specific agonist endomorphin-1 altered interleukin-8 (IL-8) production by Caco-2 cells. Using RT-PCR and immunocytochemistry, Caco-2 cells were found to constitutively express (mu) mu opioid receptors. Activation of the mu receptor by endomorphin-1 (1 and 10 microM) resulted in significant increases in IL-8 when Caco-2 cells were stimulated with IL-1beta. Increased IL-8 secretion due to endomorphin-1 could be blocked by pre-incubating cells with the mu receptor antagonist, beta-funaltrexamine. These results indicate that the intestinal epithelial IL-8 response can be altered by a muopioid receptor mediated mechanism.