Raf-1 without MEK?

The Ras-Raf-MEK [(mitogen-activated protein kinase (MAPK) or extracellular signal-regulated kinase (ERK) kinase]-MAPK signaling pathway controls the activation of many cellular functions. Recent reports of Raf-1-deficient mice have indicated that MEK may not be an important downstream substrate for Raf-1 and that, in fact, Raf-1 is important for blocking apoptosis rather than for cell proliferation. Murakami and Morrison examine these recent findings and discuss their implications, as well as other possible conclusions that may be drawn from the published data.

Mos positively regulates Xe-Wee1 to lengthen the first mitotic cell cycle of Xenopus.

Several key developmental events occur in the first mitotic cell cycle of Xenopus; consequently this cycle has two gap phases and is approximately 60-75 min in length. In contrast, embryonic cycles 2-12 consist only of S and M phases and are 30 min in length. Xe-Wee1 and Mos are translated and degraded in a developmentally regulated manner. Significantly, both proteins are present in the first cell cycle. We showed previously that the expression of nondegradable Mos, during early interphase, delays the onset of M phase in the early embryonic cell cycles. Here we report that Xe-Wee1 is required for the Mos-mediated M-phase delay. We find that Xe-Wee1 tyrosine autophosphorylation positively regulates Xe-Wee1 and is only detected in the first 30 min of the first cell cycle. The level and duration of Xe-Wee1 tyrosine phosphorylation is elevated significantly when the first cell cycle is elongated with nondegradable Mos. Importantly, we show that the tyrosine phosphorylation of Xe-Wee1 is required for the Mos-mediated M-phase delay. These findings indicate that Mos positively regulates Xe-Wee1 to generate the G2 phase in the first cell cycle and establish a direct link between the MAPK signal transduction pathway and Wee1 in vertebrates.

Cancer of the larynx: correlation of clinical characteristics, site of origin, stage, histology and diagnostic delay.

The authors studied the records of 108 cases of cancer of the larynx registered at the Department of Otolaryngology--Clinics Hospital--Faculty of Medicine of University of São Paulo, from 1985 to 1995. Dysphonia was the most common symptom observed (85.2%), independently of the site of the tumor. Dysphagia, dyspnea and weight loss had a similar incidence (32.4%; 34.3%; and 29.6%, respectively), with dysphagia more frequent in tumors which affected the supraglottis and dyspnea in glottic and subglottic tumors. As to staging, 45.8% presented at stage IV at the first consultation, and only 13.5% at stage I. No association was observed between tumor size (according to the TNM classification), presence of lymph node involvement, and delay, in diagnosis, taking the period between the beginning of symptoms and the first consultation at the hospital. In relation to the presenting symptom those with dysphonia sought medical help later. There was no correlation between histological invasion and tumor stage. It was concluded that the stage at presentation of tumors of the larynx is possibly more related to intrinsic differences in the tumor's aggressiveness and in host characteristics than to the diagnostic delay, and that it is necessary to warn the population about symptoms which may suggest the presence of cancer of the larynx.

Analysis of the early embryonic cell cycles of Xenopus; regulation of cell cycle length by Xe-wee1 and Mos.

In Xenopus, cdc2 tyrosine phosphorylation is detected in the first 60-75 minute cell cycle but not in the next eleven cell cycles (cycles 2-12) which are only 30 minutes long. Here we report that the wee1/cdc25 ratio increases before the first mitotic interphase. We show that the Xe-wee1 protein is absent in stage VI oocytes and is expressed from meiosis II until gastrulation. A dominant negative form of Xe-wee1 (KM wee1) reduced the level cdc2 tyrosine phosphorylation and length of the first cycle. However, the ratio of wee1/cdc25 did not decrease after the first cycle and therefore did not explain the lack of cdc2 tyrosine phosphorylation in, nor the rapidity of, cycles 2-12. Furthermore, there was no evidence for a wee1/myt1 inhibitor in cycles 2-12. We examined the role of Mos in the first cycle because it is present during the first 20 minutes of this cycle. We arrested the rapid embryonic cell cycle (cycle 2 or 3) with Mos and restarted the cell cycle with calcium ionophore; the 30 minute cycle was converted into a 60 minute cycle, with cdc2 tyrosine phosphorylation. In addition, the injection of a non-degradable Mos (MBP-Mos) into the first cycle resulted in a dramatic elongation of this cycle (to 140 minutes). MBP-Mos did not delay DNA replication or the translation of cyclins A or B; it did, however, result in the marked accumulation of tyrosine phosphorylated cdc2. Thus, while the wee1/cdc25 ratio changes during development, these changes may not be responsible for the variety of cell cycles observed during early Xenopus embryogenesis. Our experiments indicate that Mos/MAPK can also contribute to cell cycle length.

Septic thrombosis of orbital vessels due to cutaneous nasal infection.

The authors describe two cases of cutaneous nose infection that quickly spread and extended to the orbital venous complex. At first glance, the clinical presentation could be mistaken for a complicated sinusal infection; therefore, the evaluation of the sinuses, by means of physical examination and radiological investigation, was of great concern, showing that there was no important pathology in the sinuses. The CT scan and the color Doppler imaging (orbital ultrasound with Doppler) demonstrated, throughout the development of the disease, that the superior ophthalmic vein was affected in both patients and the cavernous sinus in one of them. On physical examination, chemosis of the conjunctiva, proptosis, and edema of the eyelids were prominent. Patients improved only after appropriate intravenous antibiotic therapy against staphylococcus (clindamycin) and corticosteroids, making one conclude that treatment of this disease should be initiated as soon as possible in order to decrease morbidity and mortality.

Similarities between somatic cells overexpressing the mos oncogene and oocytes during meiotic interphase.

The mos protooncogene encodes a serine/threonine kinase and is a key regulator of oocyte meiotic maturation. After acute infection of Swiss 3T3 cells with virus containing the v-mos oncogene, cells expressing high levels of v-Mos round up and detach from the monolayer (floating cells), while cells that remain attached express 10-fold lower levels of v-Mos and are transformed. The floating cells are growth arrested with their chromosomes partially condensed in the absence of histone H1 kinase activity, while mitogen-activated protein kinase activity is very high. Collectively, these properties are similar to properties observed in maturing oocytes between meiosis I and II. In v-mos-transformed cell populations, mitogen-activated protein kinase activity is also elevated, correlating with the degree of morphological transformation and the level of Mos expression. Moreover, phosphoprotein modifications specific for M are found in both the floating cells and in v-mos-transformed cells, regardless of their cell cycle stage. One explanation for both morphological transformation and the phenotypes of the floating cells is that Mos imposes a meiotic program on different stages of the somatic cell cycle. The extent of this meiotic phenotype is proportional to the level of v-Mos expression. These results suggest that both morphological transformation and the phenotypes of the floating cells induced by Mos in Swiss 3T3 cells are related to its normal activities during oocyte maturation.

Signal transduction by Fc gamma RIII (CD16) is mediated through the gamma chain.

To determine the functional role of the two isoforms of Fc gamma RIII (CD16) (IIIA, IIIB), the signal transduction capabilities of wild-type and mutant forms of these receptors were analyzed in transfected lymphoid, myeloid, and fibroblastic cell lines. Functional reconstitution of receptor signalling was observed in hematopoietic T and mast cells, and was absent in nonhematopoietic (CHO) cells. Fc gamma RIIIA, a hetero-oligomeric receptor composed of a ligand-binding subunit alpha and dimeric gamma chains, generated both proximal and distal responses in Jurkat and P815 cells, typical of what is seen in natural killer cells and macrophages upon receptor activation. In contrast, Fc gamma RIIIB, which is normally attached to the cell surface via a glycosyl-phosphatidylinositol anchor, was incapable of transducing signals. After crosslinking, Fc gamma RIIIA signalling was dependent only upon the gamma chain. Fc gamma RIIIA chimeras in which the alpha subunit transmembrane and cytoplasmic domains were substituted with the corresponding gamma chain sequences functioned as well as wild-type hetero-oligomeric receptors. These data indicate that the ability of the Fc gamma RIIIA complex to activate the appropriate pathways for cell activation is cell-type restricted and independent of the transmembrane and cytoplasmic domains of the alpha subunit. The presence of the gamma chain is responsible for the assembly of, as well as the signal transduction by, the functional cell surface complex.

The role of insulin receptor autophosphorylation in signal transduction.

We have examined the role of autophosphorylation in insulin signal transmission by oligonucleotide directed mutagenesis of seven potential tyrosine autophosphorylation sites in the human insulin receptor. Chinese hamster ovary cells transfected with these receptors were analyzed for insulin stimulated 2-deoxyglucose uptake, thymidine incorporation, endogenous substrate phosphorylation, and in vitro kinase activity. We found that phosphorylation on tyrosine residues 953, 1316, and 1322 were not necessary for receptor-mediated signal transduction. Mutation of tyrosine 960 reduced but did not abolish the signaling capabilities of the receptor. Finally, the simultaneous mutation of tyrosine residues 1146, 1150, and 1151 (the numbering system is that of Ullrich et al. (Ullrich, A., Bell, J. R., Chen, E. Y., Herrera, R., Petruzzelli, L. M., Dull, T. J., Gray, A., Coussens, L., Liao, Y. C., Tsubokawa, M., Mason, A., Seeburg, P.H., Grunfeld, C., Rosen, O. M., and Ramachandran, J. (1985) Nature 313, 756-761) resulted in a biologically inactive receptor, suggesting that the insulin receptor can be inactivated by removal of key autophosphorylation sites.