The histidine kinase-related domain participates in phytochrome B function but is dispensable.

Phytochromes are photoreceptors that control many plant light responses. Phytochromes have two carboxyl-terminal structural domains called the PAS repeat domain and the histidine kinase-related domain. These domains are each related to bacterial histidine kinase domains, and biochemical studies suggest that phytochromes are light-regulated kinases. The PAS repeat domain is important for proper phytochrome function and can interact with putative signaling partners. We have characterized several new phytochrome B mutants in Arabidopsis that express phyB protein, three of which affect the histidine kinase-related domain. Point mutations in the histidine kinase-related domain cause phenotypes similar to those of null mutants, indicating that this domain is important for phyB signaling. However, a truncation that removes most of the histidine kinase-related domain results in a phyB molecule with partial activity, suggesting that this domain is dispensable. These results suggest that phytochromes evolved in modular fashion. We discuss possible functions of the histidine kinase-related domain in phytochrome signaling.

Targeted in vivo expression of the cyclin-dependent kinase inhibitor p21 halts hepatocyte cell-cycle progression, postnatal liver development and regeneration.

The CDK inhibitor p21 (WAF-1/CIP-1/SDI-1) has been implicated in DNA damage-induced p53-mediated G1 arrest, as well as in physiological processes, such as cell differentiation and senescence, that do not involve p53 function. To determine the impact of p21 on normal development and cell-cycle regulation in vivo, we have generated transgenic mice that abundantly express p21 specifically in hepatocytes. During postnatal liver development, when transgenic p-21 protein becomes detectable, hepatocyte proliferation is inhibited dramatically. This disturbance causes a reduction in the overall number of adult hepatocytes, resulting in aberrant tissue organization, runted liver and body growth, and increased mortality. The transgenic p21 protein is associated with most, if not all, of the cyclin D1-CDK4 in liver but not significantly with other cyclin/CDK proteins, indicating the importance of cyclin D1-CDK4 function in normal liver development. The appearance of large polyploid nuclei in some hepatocytes indicates that p21 may also cause arrest during the G2 phase of the cell cycle. Significantly, partial hepatectomy failed to stimulate hepatocytes to proliferate in p21 transgenic animals. These results provide the first in vivo evidence that appropriate p21 levels are critical in normal development and further implicate p21 in the control of multiple cell-cycle phases.

The history of diabetes lay associations.

With much of the developed world having the increasing sociologic and economic problems of an aging population, there is an increased awareness of educating patients to not only understand and follow the instructions of their medical teams but to have increased responsibility for their own care. Of all the chronic conditions, diabetes, for which there is no cure, is among the most expensive and education-intensive. The lifelong Type I insulin-dependent diabetics need to know how to adjust their life-style and activities but also how to take and adjust several times daily insulin injections, diet and exercise and how to keep a wary eye to avoid complications that might be life-threatening. Since individual instruction is not possible for the 100 million diabetics in the known world, this can be best accomplished by educating in groups.

p53-dependent apoptosis suppresses tumor growth and progression in vivo.

To determine the contribution of p53 loss to tumor progression, we have induced abnormal proliferation in the brain choroid plexus epithelium of transgenic mice using a SV40 T antigen fragment that perturbs pRB family function but does not affect p53 function. Tumors induced by this mutant develop slowly compared with those induced by wild-type T antigen. Suppressed tumor growth is directly attributable to p53 function, since rapid tumor development occurs when the T antigen fragment is expressed in p53-null mice. In p53-heterozygous mice, stochastic loss of the wild-type p53 allele results in the focal emergence of aggressive tumor nodules characteristic of tumor progression. In each case, aggressive tumor development in the absence of p53 function corresponds to a decrease in the level of apoptosis. These results provide in vivo evidence that p53-dependent apoptosis, occurring in response to oncogenic events, is a critical regulator of tumorigenesis.

The treatment of NIDDM in the decade of the 90s.

On the occasion of the introduction of gliclazide (Diamicron) in Canada, it seems useful to assess the use of oral hypoglycemics in the treatment of NIDDM. Various types of diabetes occur when insufficient insulin is produced or when various factors reduce the receptor efficacy. Most of the factors involved are favorably affected by the action of sulfonylureas. Many NIDDM patients exhibit poor compliance with regard to exercise and diet, and require oral hypoglycemics. Combinations of oral hypoglycemics and insulin are very useful in patients responding poorly to either type of treatment since this gives effective insulin levels with improved receptor activity. Diamicron offers advantages since it reduces blood glucose effectively, has few side effects and no evidence of long-term problems or toxicity. Studies have shown that there is a significant antiplatelet aggregation effect and a beneficial effect on the fibrinolytic system with gliclazide (but not necessarily with other oral hypoglycemics), which may be useful in preventing or attenuating some long-term complications of diabetes, e.g. diabetic retinopathy. In a study at the Joslin Clinic, three groups of patients with NIDDM were examined: dietary failures, secondary failures with first generation oral hypoglycemics, and poorly regulated patients treated with insulin. After three months of treatment with Diamicron, all 10 dietary failure patients improved, as did three of the 10 secondary failure cases and five of the insulin-treated patients. Receptor studies indicated increased sensitivity in some cases, without a consistent change in numbers. Some patients with the poorest response to insulin alone had the best results with combined therapy, although it took almost eight weeks to achieve this.

The role of oral hypoglycemic agents in therapy and prevention of macrovascular complications.

Of all the possible atherosclerotic factors, it must be accepted that only a few can be reached by today's diabetes therapy. Control of diabetes (hopeful, but not proven); Aging--useful but only in as much as good treatment might retard the aging process (questionable); Obesity--a great generality (possibly helpful); Lipids and lipoproteins (probably helpful, although more specifics needed); Hyperinsulinism (questionable--more studies underway); Platelet changes and coagulation (probably an important area--much investigation underway); There is no real evidence that any oral hypoglycemic agent is specific for treatment in these areas. Claims are made for some of the present oral hypoglycemic agents. Are these alleged benefits due to the specific properties of these agents or are they simply reinforcement of good diabetes control? There have been some specifically favorable reports of experiments with glicazide. If these are true, this would add another important dimension to its accepted hypoglycemic role. At this time, the oral hypoglycemic agents must be considered adjuncts in good control of diabetes and as such might provide a beneficial influence on atherosclerosis and macrovascular complications, but this is hardly specific.

Glyburide (DiaBeta): a new second-generation hypoglycemic agent.

Glyburide is an improved drug for the management of non-insulin-dependent diabetes mellitus (NIDDM). It is at least as effective as the first-generation oral hypoglycemics and is effective in doses that are considerably less than those needed with first-generation sulfonyl-ureas. While its mode of action is similar to that of other agents, glyburide has the unique feature of prolonged activity despite a short half-life and short duration in the body. Side effects are minimal, and toxic reactions have not been reported. While hypoglycemic episodes can occur, as with any blood glucose-lowering agent, they can be prevented by being alert to patients who may be more sensitive to oral agents. Unlike older sulfonylureas, about 50% of glyburide is excreted through the feces. In 14 years of worldwide experience, glyburide has rarely shown disulfiram-like effects and has not shown antidiuretic effects. While glyburide produces an insulin release response to glucose that parallels a normal physiological response, it appears to also decrease resistance to insulin and sensitize the receptors while utilizing the patient's available endogenous insulin. There are two major metabolites, but they are inert and are rapidly excreted, having no hypoglycemic effect. Considering the safety of glyburide and the large worldwide population that uses this agent, it is expected that this new second-generation hypoglycemic agent will greatly increase the therapeutic spectrum for NIDDM. Not only is it possible for more patients with diabetes to be treated, but many already being treated orally can achieve better regulation with this effective new oral agent.

Oral hypoglycemic agent update.

The treatment of diabetes is still a problem more than a half-century after the discovery of insulin. Patients are now living significantly longer but until the development of oral hypoglycemic agents, the only direct treatment modalities were exercise, diet, and insulin. Before evaluating the effectiveness of treatment, a therapeutic goal must be determined. While there are no absolutely "hard" facts proving that "good control" is beneficial in preventing chronic complications of diabetes, increasing accumulation of "soft" data strongly suggests that normal blood glucose levels are most desirable, when possible, but not at the cost of severe or disabling hypoglycemic reactions. The development of the oral agents was a great public health advance in that many persons with early diabetes, but fearful of insulin injections, had less dread of "the pills" and sought treatment. The oral agents simplified care but this very simplification process often undermined the need for proper diet and good fundamental care. This often led to mediocre diabetes care. While useful, the oral agents have marked limitations and in some are effective only temporarily. The presently available oral agents are sulfonylureas and require a viable beta-cell system for success. This limits the number of diabetics responsive to such treatment. The general indications for tolbutamide, chlorpropamide, acetohexamide and tolazamide are in maturity-onset diabetics, generally beyond the age of 40 with diabetes of less than 10 years. They are contraindicated in juvenile-onset diabetics, in pregnant women, and usually in patients undergoing major surgery, and can become ineffective during periods of extreme stress or during severe infection. They can lower blood glucose levels if used in proper doses in properly selected patients. Contrary to several decades of documentation, it has become popular to suggest that the oral agents are not effective. They can be effective but for many reasons apparently were not in their use by the U.G.D.P. researchers. This might not be the fault of the oral agent used. If ineffective, they should be discontinued. Many, but not all, patients may respond to diet therapy, which is then the treatment of choice. Obviously insulin, though difficult to use for many persons and in itself able to induce several severe reactions if not used properly, is the only treatment (with diet) for the severe diabetic. There is a large spectrum of patients inbetween in whom the oral agents may be useful. The use of phenformin (phenethyl-biguanide) has been effectively curtailed because of many reported cases of lactic acidosis, and while it is doubtful that phenformin alone, in the absence of complicating factors, is the causative factor, it is capable of being an augmenting influence when other conditions, such as decreased kidney function, prevail...