[Cardiogenic shock due to acute myocarditis complicating leptospirosis]

A 48 year old man was admitted to the intensive care unit with septicaemic shock associated with febrile jaundice and anuric renal failure. Within hours, he developed cardiogenic shock with multi-organ failure due to an acute myocarditis refractory to catecholamines and requiring intra-aortic balloon pumping. The diagnosis was an ictero-haemorrhagic leptospirosis, the outcome of which was finally favourable. Myocarditis is an underestimated complication of leptospirosis because it is often symptomless. The main signs are arrhythmias, conduction defects and ST-T wave abnormalities which have little clinical expression. The disease may progress and is sometimes fatal. Leptospirosis myocarditis should therefore be carefully considered because of its potential severity and its reversibility with appropriate antibiotic therapy and also the necessity of initial management in a specific infrastructure.

A role for Grb2 in apoptosis?

Src homology type 2 (SH2) and type 3 (SH3) domains appear to have an important role in signal transduction pathways initiated by tyrosine kinases. SH2 domains allow proteins with signalling functions to interact with tyrosine kinases and tyrosine-phosphorylated proteins at the plasma membrane, whereas SH3 domains allow a distinct type of interaction through binding to proline-rich sequences. The adaptor protein Grb2 consists of one SH2 domain and two SH3 domains and connects tyrosine kinase receptors to activation of the Ras pathway. Its closely related counterpart, Grb3-3, thought to arise by alternative splicing of Grb2 transcripts, lacks a functional SH2 domain but retains functional SH3 domains. We recently presented evidence that Grb3-3 might deliver specific signals causing cells to undergo apoptosis. This review will document the mechanism of Grb3-3 function and discuss its putative involvement in several pathologies. It also further strengthens the notion that cells may use alternative splicing as a means to drive either a proliferative or a suicidal program.

Cloning of a Grb2 isoform with apoptotic properties

Growth factor receptor-bound protein 2 (Grb2) links tyrosine-phosphorylated proteins to a guanine nucleotide releasing factor of the son of sevenless (Sos) class by attaching to the former by its Src homology 2 (SH2) moiety and to the latter by its SH3 domains. An isoform of grb2 complementary DNA (cDNA) was cloned that has a deletion in the SH2 domain. The protein encoded by this cDNA, Grb3-3, did not bind to phosphorylated epidermal growth factor receptor (EGFR) but retained functional SH3 domains and inhibited EGF-induced transactivation of a Ras-responsive element. The messenger RNA encoding Grb3-3 was expressed in high amounts in the thymus of rats at an age when massive negative selection of thymocytes occurs. Microinjection of Grb3-3 into Swiss 3T3 fibroblasts induced apoptosis. These findings indicate that Grb3-3, by acting as a dominant negative protein over Grb2 and by suppressing proliferative signals, may trigger active programmed cell death.

R-ras interacts with rasGAP, neurofibromin and c-raf but does not regulate cell growth or differentiation

Within the superfamily of ras-related GTP-binding proteins, only ras itself has been shown to act as an oncogene. Seven other proteins, however, have greater than 50% amino acid identity to ras and one of them, rap1A, has been shown to interact with the ras GTPase activating protein, ras-GAP, and to inhibit ras function when overexpressed. In this paper, we have examined the biological and biochemical activities of another close relative of ras, R-ras. We show that in vitro, R-ras shares a number of activities with ras; it interacts with the catalytic domain of ras-GAP, with the GAP-related domain of neurofibromin and with the ser/thr kinase, c-raf. Furthermore, R-ras stimulates the expression of c-fos when microinjected into Swiss 3T3 cells. However, unlike ras, R-ras does not include DNA synthesis or membrane ruffling in quiescent fibroblasts, nor does it induce maturation of Xenopus oocytes or differentiation of PC12 cells. In addition, we show that unlike rap1A, R-ras does not interfere with ras-stimulated gene transcription. We conclude from these experiments that although R-ras and ras share some biochemical activities, they control distinct biological processes.

Tumour suppressors and the regulation of GTP-binding protein activity

GTP-binding proteins regulate a wide variety of intracellular signalling pathways in eukaryotic cells. The Ras GTP-binding proteins have received a great deal of attention since they were found to be modified by amino acid substitutions in a large number of cancers. It is now clear that Ras plays an essential role in regulating normal cell growth and differentiation, although how this is achieved biochemically is not known. The cellular concentration of Ras bound to GTP appears to be the limiting factor for signalling, and, not surprisingly, it is tightly controlled by both positive and negative regulators. There is now convincing evidence that the loss of one of these negative regulators of Ras, neurofibromin, can contribute to the development of malignancy; thus, neurofibromin behaves as a tumour suppressor gene product.

Short modified antisense oligonucleotides directed against Ha-ras point mutation induce selective cleavage of the mRNA and inhibit T24 cells proliferation

We have used derivatized antisense oligodeoxynucleotides both in vitro and in vivo specifically to inhibit translation of the activated human oncogene Ha-ras. The oligonucleotides (5'-CCACACCGA-3') were targeted to a region of Ha-ras mRNA including the point mutation G----T at the 12th codon which leads to a Gly----Val substitution in the ras p21 protein. They were linked to an intercalating agent and/or to a hydrophobic tail, both to increase their affinity for their mRNA target and to enhance their uptake by tumor cells. A cell-free translation system was used to demonstrate an RNase H-dependent specific inhibition of activated ras protein synthesis. 50% inhibition was observed at a concentration of 0.5 microM of the most efficient oligonucleotide (5'-substitution with an acridine derivative and 3'-substitution by a dodecanol chain). This inhibitory effect stems from a point mutation-sensitive cleavage of the mRNA and it mirrors the growth inhibition obtained with T24 bladder carcinoma cells, which carry activated Ha-ras. The proliferation of HBL100 cells (non tumorigenic human mammary cell line) which carry two copies of normal Ha-ras was unaffected. This study shows that it is possible to design antisense agents that will inactivate the mutated oncogene but not the protooncogene which is generally essential to cell survival.

The COOH-domain of the product of the Saccharomyces cerevisiae SCD25 gene elicits activation of p21-ras proteins in mammalian cells

The evidence presented here indicates that the domain containing the COOH-terminal part of the Saccharomyces cerevisiae SCD25 gene product (C-domain), which is homologous to the COOH-terminal part of CDC25 protein, can elicit activation of mammalian ras proteins in CHO cells. Transfection of expression vectors carrying the C-domain of SCD25, but not of CDC25, promotes the GTP-bound form of ras proteins as determined by analysis of the guanine nucleotides bound to ras proteins immunoprecipitated by Y13-259 mAb, and enhances transcription of a HIV-LTR-CAT construct. This is the first demonstration of the activation of ras proteins by transfection of a single heterologous gene.

Oncogenic proteins new targets for chemotherapeutic agents against cancer

Over the past 10 years, more than 40 potentially oncogenic genes, termed protooncogenes, have been identified in the human genome. Little is known of the physiological role of the proteins encoded by these genes, but they seem to be involved in the reception and transmission of hormonal and other environmental information from the cell membrane to the nucleus. These proteins may acquire transforming properties when over-expressed or if structurally altered following partial deletions or point mutations. Cytogenetic analysis shows loss of genetic material from specific chromosomal loci in many human tumors, suggesting that the absence of a functional gene at these loci may permit tumor development. The genes involved have been termed "anti-oncogenes". Understanding the control mechanisms of cell proliferation is essential in order to understand how cancer cells escape from this control. To this end, numerous oncogenes have been cloned, permitting the production of modified forms of oncogenic proteins and identification of the regions essential for their biological activity. Availability of large amounts of protein also allows the production of specific antibody which can be used to verify whether blockage of a given protein results in reversion of the transformed phenotype. If it can be shown that the expression of an oncogenic protein is essential for transformation, it should be possible to search for molecules that inhibit its action or which mimic the effects of an anti-oncogene. This type of research is already well advanced for the oncogenic ras proteins, and models have been established that permit both screening for potential inhibitors and design of specific antagonists.

Antibodies to synthetic peptide from the residue 33 to 42 domain of c-Ha-ras p21 block reconstitution of the protein with different effectors

Residues 32 to 40, which are conserved among ras proteins from different species, are likely to participate in interactions with the p21 effector system. With the goal of understanding the structural basis of the regulatory functions of c-Ha-ras p21, we produced rabbit antisera against a synthetic peptide corresponding to amino acids 33 to 42 of the protein. The affinity-purified antibodies interacted specifically with p21 and with the antigenic peptide. The epitope recognized by the antibodies appeared to be centered on threonine 35. The antibodies inhibited both in vitro p21-induced production of cyclic AMP in detergent extracts of RAS-defective yeast membranes and GAP-stimulated GTPase activity. However, monoclonal anti-ras antibodies Y13-259 and Y13-238 were not capable of specifically inhibiting interactions of p21 with these two putative effector proteins. The apparent inhibitory effect of Y13-259 on stimulation of p21 by GAP was due to a greatly reduced rate of exchange of nucleotides in the binding pocket of the protein. These findings provide additional support for the essential role of the residue 32 to 40 domain as the true effector site and further evidence of the involvement of GAP as a cellular effector of ras proteins.

Differential sensitivity to pertussis toxin of 3T3 cells transformed with different oncogenes

Pertussis toxin (PT), which blocks the activity of several G-proteins, has been found to exert a marked inhibitory effect on the DNA synthesis induced in 3T3 cells by serum or growth factors. 3T3 cells transformed with human c-ras oncogenes (Ha-ras, Ki-ras, N-ras) or with src, an oncogene coding for a protein kinase, have lost sensitivity to growth control by PT, even though substrates for PT can still be ADP-ribosylated in vivo. In contrast, 3T3 cells transformed with the SV40 virus behave like normal untransformed cells with respect to the ability of PT to decrease their growth rate. Oncogenes can thus likely be classified either as 'responders' or 'non-responders' to PT.

Maturation of the hypothalamo-pituitary-ovarian axis in adolescent girls

The first menstrual cycles after menarche are irregular and anovulatory. To determine whether these cycles reflect immature pituitary responsiveness to gonadotropin-releasing hormone (GnRH) in relationship to ovarian steroid secretion, we measured basal plasma estradiol (E2), progesterone (P), and gonadotropins as well as LH and FSH responses to GnRH in 90 healthy girls during the first 5 yr after menarche. During the first year postmenarche, sex steroids, basal gonadotropins, and responses to GnRH had not yet reached adult values. During the second year, the increase in E2 was accompanied by a higher secretion of gonadotropins, both basally and in response to GnRH, which was similar to that observed in control adult women during both phases of the menstrual cycle, although P remained low. From the third to the fifth postmenarchal years, there was a progressive increase in the luteal LH and FSH responses to GnRH, resulting in significantly higher responses than in adult controls. Despite the progressive increase in sex steroids there was still a low percentage of ovulatory cycles over the 5 postmenarchal yr (0-63%). When the data were classified according to luteal P levels, it was found that anovulatory cycles (P less than 0.9 ng/ml) with normal E2 levels (100 pg/ml) resulted in exaggerated responses to GnRH, while in ovulatory cycles with P levels greater than 10 ng/ml and normal E2 concentrations, a lower response was observed, suggesting that high concentrations of P exerted a negative feedback on LH and FSH secretion. In contrast, the association of lower E2 (less than 100 ng/ml) and P (less than 5 ng/ml) levels resulted in a synergistic positive action on gonadotropin secretion. These data extend to endogenous sex steroids the dose-dependent positive and negative actions on gonadotropin secretion previously demonstrated with exogenously administered steroids in women.

[Gynecologic disorders in the prevention of juvenile diabetes]

Repeated gynecological affections have been detected in 26 out of 30 diabetic children. Therefore, it is important to do gynecological examinations in diabetic children. In addition, during a systematic check out, an impaired glucose tolerance has been found in 7 out of 18 children who presented inflammatory and itching gynecological affections. These findings emphasize the importance of systematical gynecological examination in childhood and adolescence in preventive medicine.