PubMed Health⌕ Search

Biomedical subjects

M S Rubin

Publications and source records attributed to M S Rubin.

At least 19 recordsLinked to original sources
PubMed1996

Formation of p27-CDK complexes during the human mitotic cell cycle.

In eukaryotic cells, the coordinated activation of different cyclin-dependent kinases regulates entry into S-phase. In vitro and in nonproliferating cells, p27 associates with and inhibits cyclin/cycin-dependent kinase (CDK) holoenzymes containing either CDK4, CDK6, or CDK2. Although many different types of proliferating cells contain p27 protein, neither the interactions of p27 with cyclin/CDK complexes nor the consequences of this interaction during the mitotic cycle have been fully explored. We report that, in MANCA cells, the amount of p27 is constant during the cell cycle. In addition, p27 associates with three different CDKs: CDK2, CDK4, and CDK6. Furthermore, the amount of p27 is significantly lower than the amount of cyclin D3 in these cells. The amount of CDK4 and CDK6 associated with p27 does not change in a cell cycle-dependent fashion; in contrast, the amount of CDK2 associated with p27 is lowest in early G1 cells and increases to a maximum in mid-G1 phase, reaching a steady-state level in late G1-phase cells. After mid-G1 phase, the amount of each p27/CDK complex remains constant through the remainder of the cell cycle. p27-immunoprecipitates contain an Rb-kinase activity. The substrate specificity, the expression pattern of this kinase, and the ability to deplete 50% of this kinase activity with a CDK6-specific antibody suggest that the CDK6 protein mediates, in part, the p27-associated Rb-kinase activity. In contrast, p27 complexes containing CDK2 are incapable of phosphorylating histone H1. These data are consistent with a model wherein cyclin D/CDK complexes sequester the CDK2-dependent kinase inhibitory activity of p27.

Animals↗
PubMed1995

Insulin-like growth factors modulate the growth inhibitory effects of retinoic acid on MCF-7 breast cancer cells.

Retinoids are currently being tested for the treatment and prevention of several human cancers, including breast cancer. However, the anti-cancer and growth inhibitory mechanisms of retinoids are not well understood. All-trans retinoic acid (RA) inhibits the growth of the estrogen receptor-positive (ER+) breast cancer cell line, MCF-7, in a reversible and dose-dependent manner. In contrast, insulin-like growth factors (IGF-I, IGF-II) and insulin are potent stimulators of the proliferation of MCF-7 and several other breast cancer cell lines. Pharmacologic doses of RA (> or = 10(-6) M) completely inhibit IGF-I-stimulated MCF-7 cell growth. Published data suggest that the growth inhibitory action of RA on IGF-stimulated cell growth is linear and dose-dependent, similar to RA inhibition of unstimulated or estradiol-stimulated MCF-7 cell growth. Surprisingly, we have found that IGF-I or insulin-stimulated cell growth is increased to a maximum of 132% and 127%, respectively, by cotreatment with 10(-7) M RA, and that 10(-9) - 10(-7) M RA increase cell proliferation compared to IGF-I or insulin alone. MCF-7 cells that stably overexpress IGF-II are also resistant to the growth inhibitory effects of 10(-9) - 10(-7) M RA. Treatment with the IGF-I receptor blocking antibody, alpha IR-3, restores RA-induced growth inhibition of IGF-I-treated or IGF-II-overexpressing MCF-7 cells, indicating that the IGF-I receptor is mediating these effects. IGFs cannot reverse all RA effects since the altered cell culture morphology of RA-treated cells is similar in growth-inhibited cultures and in IGF-II expressing clones that are resistant to RA-induced growth inhibition. These results indicate that RA action on MCF-7 cells is biphasic in the presence of IGF-I or insulin with 10(-9) - 10(-7) M RA enhancing cell proliferation and > or = 10(-6) M RA causing growth inhibition. As IGF-I and IGF-II ligands are frequently detectable in breast tumor tissues, their potential for modulation of RA effects should be considered when evaluating retinoids for use in in vivo experimental studies and for clinical purposes. Additionally, the therapeutic use of inhibitors of IGF action in combination with RA is suggested by these studies.

Breast Neoplasms↗
PubMed1995

Severe Clostridium difficile colitis.

PURPOSE: Reports of fatality related to Clostridium difficile colitis and a sharp increase in prevalence of this infection prompted a study of patients who develop a more aggressive form of this disease. METHODS: Over 38 months, 710 patients at our institution developed C. difficile colitis. Twenty-one (3 percent) of these patients either required intensive care unit admission or died as a result of their infection. A retrospective, case-controlled study was undertaken to compare these patients, who were considered to have severe C. difficile colitis, with the remaining patients with milder disease. RESULTS: Factors that predisposed to the development of severe C. difficile colitis included intercurrent malignancy, chronic obstructive pulmonary disease, immunosuppressive and antiperistaltic medications, renal failure, and administration of clindamycin (P < 0.05 for all). Patients with severe C. difficile colitis were more likely to have abdominal pain, tenderness and distention, peritonitis, hemoconcentration (> 5 points), hypoalbuminemia (< 3 mg/dl), and elevated or suppressed white blood cell count (> 25,000; < 1,500; P < 0.05 for all). These factors were used to create a scoring system that could distinguish between patients with severe C. difficile colitis and those with mild disease. Thirteen patients in the late stages of terminal illness with metastatic malignancy or age > 90 were considered poor or inappropriate surgical candidates. Only the remaining eight patients could have potentially recovered from operation with hope for long-term survival. Of these, seven were treated without colonic resection, and six of the seven survived, whereas one patient underwent colectomy and did not survive. CONCLUSIONS: Patients with severe C. difficile colitis can be readily identified. Often they have coexisting illness that precludes operation. In this series, only 1 of 21 patients with severe C. difficile might have benefited from an aggressive surgical approach.

Age Factors↗
PubMed1994

Parastomal hernia. Is stoma relocation superior to fascial repair?

OBJECTIVE: To evaluate methods of parastomal hernia repair. DESIGN: Retrospective analysis. SETTING: Two tertiary care institutions. PATIENTS: Eighty patients undergoing 94 parastomal hernia repairs between 1983 and 1991. INTERVENTIONS: Three methods of repair were examined: fascial repair, stoma relocation, and fascial repair with prosthetic material. MAIN OUTCOME MEASURE: Parastomal hernia recurrence and short- and long-term complications. RESULTS: Fifty-five (93%) of 59 living patients were available and examined at a median of 31.5 months following repair, providing 68 repairs for consideration. Fascial repair was used in 36 cases, stoma relocation in 25 cases, and fascial repair with prosthetic material in seven cases. Overall, 63% of patients developed a recurrent parastomal hernia and 63% had at least one postoperative complication. Following first-time repair, parastomal hernia recurrence developed in 22 (76%) of 29 patients who had fascial repair but in only six (33%) of 18 patients who had stoma relocation (P < .01). When repair was undertaken for recurrent parastomal hernia, fascial repair failed in all seven cases, stoma relocation failed in five (71%) of seven cases, and fascial repair with prosthetic material failed in one (33%) of three cases. The only factor that significantly affected the recurrence rate was the technique of repair. Complications were more common following stoma relocation (88%) than following fascial repair (50%) (P < .05). In particular, incisional hernias developed in 52% of patients following stoma relocation but in only 3% of patients following fascial repair. When postoperative occurrence of all abdominal-wall hernias was compared, there was no significant difference between the fascial repair group (29 [81%] of 36 repairs) and the stoma relocation group (17 [68%] of 25 repairs). Furthermore, the reoperation rate for hernia repair was nearly identical (31% vs 28%) between these two groups. CONCLUSIONS: Parastomal hernia repair is often unsuccessful and rarely without complication. For first-time parastomal hernia repairs, stoma relocation is superior to fascial repair. For recurrent parastomal hernias, repair with prosthetic material is the most promising of a group of poor alternatives.

Adult↗
PubMed1993

Legal considerations in cases of child abuse.

Child abuse is a common pediatric problem that can be recognized and treated appropriately by all primary care physicians who care for children. One of the necessary skills in this process involves being prepared to interface with the legal system. The physician is mandated to report suspected child abuse according to his or her state laws. He or she must be aware of the legal recourses for child protection in cases when the child remains at risk. When interacting with the child, a number of legal considerations can guide the physician in obtaining information with history, physical examination, and specimen collection. Finally, the physician may be called to testify. An understanding of how to prepare for court and how to conduct oneself in court is the final necessary skill for the primary care physician who sees children. This article provides the primary care physician with a practical understanding of the legal considerations in child abuse.

Child↗
PubMed1986

Isolation and characterization of granules of the toad bladder.

The electron-dense granules that lie just below the apical plasma membrane of granular epithelial cells of toad urinary bladder contribute glycoproteins to that apical membrane. Also, exocytosis of granules (and tubules) elicited by antidiuretic hormone potentially doubles that apical surface, during the same period the transport changes characteristic of the hormonal response occur. Granules separated from other membrane systems of the cells provide the material to assess the importance of the granules as glycocalyx precursors and in hormone action. We used isosmotic media to effect preliminary separations by differential centrifugation. Then granules were isolated by centrifugation on self-forming gradients of Percoll of decreasing hypertonicity. We find qualitative and quantitative changes in protein composition and enzymic activities in the isolated fractions. The primary criterion for granule purification was electron microscopic morphology. In addition, polypeptide species found in the granule fraction are limited in number and quantity. The granules are enzymically and morphologically not lysosomal in nature. Granules may provide the glycoproteins of the apical glycocalyx but they differ from the isolated plasma membrane fraction enzymically, in protein composition and in proportion of esterified cholesterol. We conclude that the granules are not "average" plasma membrane precursors. Their role in the membrane properties of the toad urinary bladder may now be evaluated by characterizing permeability and other properties of the isolated organelles.

Adenosine Triphosphatases↗
PubMed1984

Maximal flux responses after multiple challenges with vasopressin.

Antidiuretic hormone (ADH) increases transepithelial flux of water and particular solutes across the amphibian urinary bladder and mammalian collecting duct by increasing the permeability of the apical surface. We find that if each challenge with ADH is ended by replacing the medium bathing both the mucosal and serosal surfaces of the toad bladder, then rechallenge with the same supramaximal dose of ADH 36-100 min later produces flux equivalent to or greater than the original response, but rechallenge after 15 min produces only 68% of the original response. If the medium bathing the mucosal surface is neither replaced nor returned to its original volume, complete recovery of the osmotic flux response to ADH does not occur. Maximal restimulation by ADH occurs with transepithelial osmotic gradients between 119 and 180 mosmol/kg during both challenges (the serosal bath is always isotonic amphibian Ringers). In addition, ADH-containing serosal baths that have maximally activated transport across bladders for 30-60 min can be reused and again produce maximal activation of ADH responses in fresh bladders or in the original bladders after washing. These results are in contradistinction to reports of desensitization of transepithelial flux upon rechallenge with ADH after an initial stimulation under many conditions. Our findings suggest that desensitization in vitro may result from experimental design rather than intrinsic biological characteristics of the system.

Animals↗
PubMed1984

Effect of an osmotic gradient on antidiuretic hormone-induced endocytosis and hydroosmosis in the toad urinary bladder.

The luminal (apical) border of the epithelium of the bladder in the well-hydrated toad is relatively impermeable, so the bladder usually stores hyposmotic urine. When antidiuretic hormone (ADH) increases apical membrane osmotic permeability dramatically, water is resorbed from hyposmotic mucosal solution; in the presence of hyposmotic or isosmotic mucosal solutions, ADH concomitantly induces exocytosis at the apical border of granule-rich (G) cells. Then ADH induces endocytosis at this border. We describe how an osmotic gradient affects ADH-induced endocytosis and hydroosmosis in vitro. We can assess ADH-induced endocytosis in gradient and no-gradient bladders by applying a double-marker technique that distinguishes among endocytosis, completed internalization of previously surface-attached membrane, and surface invagination by comparing the number of horseradish peroxidase (HRP) uptake bodies (endocytosis) with the number of ruthenium red (RR)-delineated bodies (surface invaginations). With this approach we find that gradient bladders have approximately six times more ADH-induced endocytosis than no-gradient bladders during 45-60 min of ADH stimulation. Furthermore, at 60 min approximately 50% of the HRP-containing structures in no-gradient bladders remain surface connected compared with approximately 1% in gradient bladders. In parallel physiological studies, no-gradient bladders reach and maintain higher induced osmotic permeabilities than gradient bladders. These findings support the hypothesis that endocytosis plays an active role in reestablishing impermeable apical surface characteristics in toad bladder.

Animals↗
PubMed1982

Membrane transport during erythroid differentiation.

Transport, unidirectional flux, of a monosaccharide, a nucleoside and three amino acids, all of which enter cells by independent, discrete carriers, was compared at three stages of erythroid maturation, the normal (anucleate) mouse erythrocyte, and in differentiated and undifferentiated Friend erythroleukemia cells. We found specific transport alterations during this developmental program. Transport of 3-O-methylglucose increased with each successive developmental stage. Aminoisobutyrate transport was maintained during Friend cell differentiation, but fell slightly in erythrocytes. Leucine, lysine and uridine transport began to fall two days after dimethylsulfoxide exposure, and diminished further in red cells. These studies of transport are not directly comparable to uptake studies reported by others. Median cell volume and thus surface area decreased more during differentiation than amino acid transport declined, so flux, transport past a unit area of membrane, actually increased. Monosaccharide flux also increased. Only uridine transport fell in parallel to surface area. Perhaps sites for nutrient transport required for energy production are preferentially maintained.

Aminoisobutyric Acids↗