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Several related isoforms of p[38.sup.MAPK] have been identified and cloned in many species. Although they all contain the dual phosphorylation motif TGY. the expression of these isoforms is not ubiquitous, p38[alpha] and -[beta]2 are ubiquitously expressed, whereas p38[gamma] and -[delta] appear to have more restricted expression. Because there is evidence for selective activation by upstream kinases and selective preference for downstream substrates, the functions of these conserved proteins is still incompletely understood. We have demonstrated that the renal mesangial cell expresses the mRNA for all the isoforms of p[38.sup.MAPK], with p38[alpha] mRNA expressed at the highest level, followed by p38[gamma] and the lowest levels of expression by p38[beta]2 and -[delta]. To determine the functional effects of these proteins on interleukin (IL)-1[beta]-induced inducible nitric oxide synthase (iNOS) expression, we transduced TAT-p38 chimeric proteins into renal mesangial cells and assessed the effects of wild-type and mutant p38 isoforms on ligand induced iNOS expression. We show that whereas p38[gamma] and -[delta] had minimal effects on iNOS expression, p38[alpha] and -[beta]2 significantly altered its expression. p38[alpha] mutant and p38[beta]2 wild-type dose dependently inhibited IL-1[beta]-induced iNOS expression. These data suggest that p38[alpha] and [beta]2 have reciprocal effects on iNOS expression in the mesangial cell, and these observations may have important consequences for the development of selective inhibitors targeting the p[38.sup.MAPK] family of proteins. TAT proteins; p38 MAPK; inducible nitric oxide synthase; mesangial cell; interleukin-1

Interleukin-1beta induces the biosynthesis of nitric oxide and prostaglandin E2 in mesangial cell cultures from rat kidneys. This induction is enhanced in the presence of insulin and insulin-like growth factor-I (IGF-I) by inducing the translation of inducible nitric oxide and cyclooxygenase. Both IGF-I and insulin also enhances the phosphorylation of the mitogen-activated protein kinase. The implications of these findings on the inflammatory processes taking place in the kidneys are discussed.

Research shows that the delta-isoform of the enzyme protein kinase C (PKC)stimulates the production of inducible cyclooxygenase (COX), prostaglandin E2, inducible nitric oxide synthase within rat mesangial cells. A retroviral vector was used to overexpress the enzyme and the results compared with mesangial cells under the influence of control retroviral vectors and untransfected mesangial cells. PKC's stimulation of COX-2 may have a direct role in inflammatory reactions.

Signal transduction by interleukin-1 beta in the renal mesangial cells is mediated by the mitogen-activated protein kinase subtype JNK. The role of JNK in activating histidine-c-jun was investigated by exposing JNK to an amino terminal c-jun domain and a mutant form alanine-substituted c-jun. Interleukin 1-beta was found to increase JNK activity, and JNK phosphorylated the amino-terminal c-jun but not the mutant c-jun.

Rat mesangial cells were incubated with recombinant human interleukin 1-beta (IL-1B) to determine if IL-1B induces gene expression of interstitial collagenase. The results show that IL-1B stimulates the synthesis and activity of interstitial collagenase. This activity of IL-1B involves tyrosine kinase signal transduction mechanisms, but not endogenous prostaglandins.

The tyrosine kinase plays a crucial role in interlukin IL-1 beta signalling to bring about the inducible form of nitric oxide synthase (iNOS) in rat mesangial cells. The study of the effect of tyrosine kinase inhibitors on IL-1 beta revealed that it induces nitrite production and iNOS mRNA expression in rat mesangial cells. Within the glomerulus the mesangial cells perform various functions including regulation of glomerular filtration, elaboration of extracellular matrix, and phagocytosis of immune complexes.

A study on the destiny of individual fatty acids bound to albumin when they are assimilated by the proximal tubular cells shows that they have distinct metabolic effects in the proximal tubular cells. Fatty acid-albumin uptake produces a marked increase in total triglyceride level. After being taken up, different fatty acids are incorporated in a characteristic fashion into certain complexes, which is dependent on the presence or absence of double bonds.

A study of the impact of the cycloxygenase (COX) suppression and exogenous prostoglandin (PG) on the generation of nitric oxide and activation of nitric oxide synthase (NOS) in rat mesangial cells reveals that the activation of NOS by interleukin 1 is downregulated by PGE2. This inhibition by PGE2 is independent of adenylated cyclase stimulation. COX inhibition decreases PGE2 release, thereby enhancing NO and NOS levels. Crosstalk between NOS and COX pathways regulates glomerular function and inflammatory process.

Gel mobility shift assays of renal mesangial cells containing interleukin-1beta (IL-1beta) reveal that IL-1beta mediates the posttranscriptional regulation of the prostaglandin endoperoxide synthase II (COX II) mRNA levels in the cells. The 3'-unsaturated region (3'-UNTR) of the COX II gene regulates the posttranscriptional response of COX II mRNA to IL-1beta levels. Two cytosolic transacting factors of 45 and 65 kDa exhibit specific binding to 3'-UNTR in a phosphorylation-dependent manner to stabilize the COX II mRNA level expression.

An analysis of the mesangial cell system reveals that interleukin-1 induces an upregulation of steady-state levels of mRNA for the prostaglandin endoperoxide synthase (PES)-2. Dexamethasone blocks the translation of the PES-2 protein. Posttranscriptional control of the message in relation to synthesis of a new protein or posttranslational alteration of elements blocking PES-2 translation, is evident.

Arachidonic acid-labeled keratinocyte cultures exposed to ultraviolet radiation were studied to determine the reason behind enhanced prostaglandin synthesis after irradiation. Results show that the rate of arachidonate liberation in irradiated cultures is nearly twice as much that in the controls. This point to the elevated phospholipase activity as the cause ofincreased prostaglandin synthesis. Irradiation did not affect cyclooxygenase activity.

Interleukin-1[Beta] (IL-1[Beta]) induces the inducible nitric oxide synthase (iNOS), resulting in the release of nitric oxide (NO) from glomerular mesangial cells. In this study, we demonstrated that disruption of F-actin formation by sequestration of G-actin with the toxin latrunculin B (LatB) dramatically potentiated IL-1[Beta]-induced iNOS protein expression in a dose-dependent manner. LatB by itself had little or no effect on iNOS expression. Staining of F-actin with nitro-benzoxadiazole (NBD)-phallacidin demonstrated that LatB significantly impaired F-actin stress fiber formation. Jasplakinolide (Jasp), which binds to and stabilizes F-actin, suppressed iNOS expression enhanced by LatB. These data strongly suggest that actin cytoskeletal dynamics regulates IL-1[Beta]-induced iNOS expression. We demonstrated that LatB decreases serum response factor (SRF) activity as determined by reporter gene assays, whereas Jasp increases SRF activity. The negative correlation between SRF activity and iNOS expression suggests a negative regulatory role for SRF in iNOS expression. Overexpression of a dominant negative mutant of SRF increases the IL-1[Beta]-induced iNOS expression, providing direct evidence that SRF inhibits iNOS expression. inducible nitric oxide synthase; serum response factor; latrunculin B; jasplakinolide; mesangial cell