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Biomedical subjects

R Civitelli

Publications and source records attributed to R Civitelli.

At least 37 records · Page 2Linked to original sources
PubMed1998

Gap junctional communication modulates gene expression in osteoblastic cells.

Bone-forming cells are organized in a multicellular network interconnected by gap junctions. In these cells, gap junctions are formed by connexin43 (Cx43) and connexin45 (Cx45). Cx43 gap junctions form pores that are more permeable to negatively charged dyes such as Lucifer yellow and calcein than are Cx45 pores. We studied whether altering gap junctional communication by manipulating the relative expression of Cx43 and Cx45 affects the osteoblast phenotype. Transfection of Cx45 in cells that express primarily Cx43 (ROS 17/2.8 and MC3T3-E1) decreased both dye transfer and expression of osteocalcin (OC) and bone sialoprotein (BSP), genes pivotal to bone matrix formation and calcification. Conversely, transfection of Cx43 into cells that express predominantly Cx45 (UMR 106-01) increased both cell coupling and expression of OC and BSP. Transient cotransfection of promoter-luciferase constructs and connexin expression vectors demonstrated that OC and BSP gene transcription was down-regulated by Cx45 cotransfection in ROS 17/2. 8 and MC3T3-E1 cells, in association with a decrease in dye coupling. Conversely, cotransfection of Cx43 in UMR 106-01 cells up-regulated OC and BSP gene transcription. Activity of other less specific osteoblast promoters, such as osteopontin and osteonectin, was less sensitive to changes in gap junctional communication. Thus, altering gap junctional permeability by manipulating the expression of Cx43 and Cx45 in osteoblastic cells alters transcriptional activity of osteoblast-specific promoters, presumably via modulation of signals that can diffuse from cell to cell. A communicating intercellular network is required for the full elaboration of a differentiated osteoblastic phenotype.

Animals↗
PubMed1998

Cyclic stretch enhances gap junctional communication between osteoblastic cells.

Mechanical loading is essential to maintain skeletal integrity. Because gap junctions in bone are affected by mechanical factors, we studied whether stretch, an anabolic stimulus for osteoblasts, modulates direct intercellular communication in these cells. Gap junctional communication during stretch was assessed using a newly developed method, the "parachute assay," which allows monitoring of dye diffusion without disruption of the plasma membrane. Application of cyclic stretch for 2 or 24 h to well-coupled ROS 17/2.8 cells resulted in a 56.5% and 30.4% increase in dye coupling, respectively, compared with resting conditions. Stretch increased dye diffusion less dramatically (12.4% compared with unstimulated cells) in the poorly coupled UMR 106-01 cells. The stretch-induced increase of cell coupling was abolished in the presence of the gap junctional inhibitor, heptanol. Steady-state mRNA levels of connexin43 (Cx43), the gap junction protein that mediates cell-to-cell diffusion of negatively charged dyes between osteoblasts, were not different between control and stretched ROS 17/2.8 or UMR 106-01 cultures after various periods of cyclic stretch. However, phosphorylated forms of Cx43 protein were more abundant in stretched ROS 17/2.8 than in controls. This was associated with increased punctate Cx43-specific immunostain at appositional membranes of stretched cells. Thus, cyclic stretch increases gap junctional communication between osteoblastic cells by modulating intracellular localization of Cx43.

Biomechanical Phenomena↗
PubMed1998

Human osteoblasts express a repertoire of cadherins, which are critical for BMP-2-induced osteogenic differentiation.

Direct cell-cell interactions are fundamental for tissue development and differentiation. We have studied the expression and function of cadherins in human osteoblasts during in vitro differentiation. Using reverse transcription-polymerase chain reaction and mRNA hybridization, we found that human trabecular bone osteoblasts (HOBs), osteoprogenitor marrow stromal cells (BMCs), and the osteogenic sarcoma lines, SaOS-2 and MG-63, expressed mRNA for cadherin-11 (C11) and N-cadherin (N-cad). HOBs and BMCs also expressed low levels of cadherin-4 (C4) mRNA. C11 was the most abundant cadherin protein present in human osteoblasts, and its expression was unaffected by bone morphogenetic protein-2 (BMP-2) treatment of either BMCs or HOBs. Likewise, N-cad mRNA did not change during BMP-2 incubation. Conversely, C4 protein, undetectable in transformed cell lines, was down-regulated by BMP-2 treatment of normal cells. Both C11 and C4 were localized to sites of cell-cell contact in both HOBs and BMCs, colocalized with beta-catenin, and bands corresponding to cadherins were coimmunoprecipitated by a beta-catenin antibody, findings indicative of functional cadherins. A decapeptide containing the HAV motif of human N-cad partially inhibited Ca2+-dependent cell-cell adhesion and completely prevented BMP-2-induced stimulation of alkaline phosphatase activity by BMCs. Thus, human osteoblasts and their progenitor cells express a repertoire of multiple cadherins. Cadherin-mediated cell-to-cell adhesion is critical for normal human osteoblast differentiation.

Bone Morphogenetic Protein 2↗
PubMed1998

Management of postmenopausal osteoporosis for primary care.

OBJECTIVE: The shift in health care delivery from a subspecialty to primary care system has transferred the responsibility of preventing osteoporotic fractures from specialists in metabolic bone disease to the web of physicians--family practitioners, general internists, pediatricians, and gynecologists--who provide the bulk of primary care. The challenge for this group of physicians is to decrease the rising prevalence of osteoporotic hip and vertebral fractures while operating within the cost parameters. It is the goal of this brief summary to provide primary practitioners with focused guidelines for the management of postmenopausal osteoporosis based on new and exciting developments. Prevention and treatment will change rapidly over the next decade and these advances will require changes in these recommendations. DESIGN: We identified patients at risk for osteoporosis and provided indications for bone mass measurement, criteria for diagnosis of osteoporosis, therapeutic interventions, and biochemical markers of the disease. RESULTS: Prevention and treatment are discussed, including hormone replacement therapy and use of calcitonin, sodium fluoride, bisphosphonates, and serum estrogen receptor modulators. CONCLUSIONS: Postmenopausal osteoporosis should no longer be an accepted process of aging. It is both preventable and treatable. Primary care physicians must proactively prevent and treat osteoporosis in their daily practice, and combination therapies are suggested.

Absorptiometry, Photon↗
PubMed1997

ATP- and gap junction-dependent intercellular calcium signaling in osteoblastic cells.

Many cells coordinate their activities by transmitting rises in intracellular calcium from cell to cell. In nonexcitable cells, there are currently two models for intercellular calcium wave propagation, both of which involve release of inositol trisphosphate (IP3)- sensitive intracellular calcium stores. In one model, IP3 traverses gap junctions and initiates the release of intracellular calcium stores in neighboring cells. Alternatively, calcium waves may be mediated not by gap junctional communication, but rather by autocrine activity of secreted ATP on P2 purinergic receptors. We studied mechanically induced calcium waves in two rat osteosarcoma cell lines that differ in the gap junction proteins they express, in their ability to pass microinjected dye from cell to cell, and in their expression of P2Y2 (P2U) purinergic receptors. ROS 17/2.8 cells, which express the gap junction protein connexin43 (Cx43), are well dye coupled, and lack P2U receptors, transmitted slow gap junction-dependent calcium waves that did not require release of intracellular calcium stores. UMR 106-01 cells predominantly express the gap junction protein connexin 45 (Cx45), are poorly dye coupled, and express P2U receptors; they propagated fast calcium waves that required release of intracellular calcium stores and activation of P2U purinergic receptors, but not gap junctional communication. ROS/P2U transfectants and UMR/Cx43 transfectants expressed both types of calcium waves. Gap junction-independent, ATP-dependent intercellular calcium waves were also seen in hamster tracheal epithelia cells. These studies demonstrate that activation of P2U purinergic receptors can propagate intercellular calcium, and describe a novel Cx43-dependent mechanism for calcium wave propagation that does not require release of intracellular calcium stores by IP3. These studies suggest that gap junction communication mediated by either Cx43 or Cx45 does not allow passage of IP3 well enough to elicit release of intracellular calcium stores in neighboring cells.

Adenosine Triphosphate↗
PubMed1997

In vitro and in vivo effects of ipriflavone on bone formation and bone biomechanics.

Ipriflavone (i.p.) positively affects bone density in postmenopausal osteoporosis, primarily by inhibiting bone resorption. Using in vitro models of human osteoblast differentiation, we have observed that i.p. and some of its metabolites stimulate the expression of bone sialoprotein, decorin, and type I collagen, and facilitate the deposition of mineralized matrix. This suggests that i.p. may stimulate bone formation in addition to its antiresorptive activity. To assess whether these effects translate into an improved bone "quality" in vivo, we measured biomechanical properties, mineral composition, and crystallinity of femurs of 12-week-old, male, Sprague-Dawley rats treated with i.p. for 1 month. i.p. significantly decreased vibration damping, an index of strain energy loss. Because vibration damping increases as bone porosity increases, the results indicate that i.p.-treated bones acquired a higher capacity to withstand dynamic stress. In fact, 1.5-fold higher energy was required to fracture femurs of i.p.-treated rats after a single supramaximal impact. i.p. also increased BMD, assessed by both volume displacement and ash analysis, whereas the relative contents of Ca, P, and Mg in the ashes were not affected. Thus, no gross abnormalities in mineral composition of bone occurred after i.p. administration. As a measure of bone crystallinity, X-ray diffraction analysis was performed. The broadening parameter beta 1/2 for the (310) and (002) reflections was not significantly different between i.p.-treated and control animals. Similarly, there were no differences in serum levels of Ca, Mg, alkaline phosphatase, and type I collagen telopeptides between treated and control animals at the end of the study. Therefore, 1-month treatment with i.p. increased bone density and improved the biomechanical properties of adult male rat bones without altering mineral composition or bone crystallinity.

Animals↗
PubMed1997

Attachment loss with postmenopausal age and smoking.

To determine whether postmenopausal bone loss and factors associated with osteoporosis affect tooth retention, we examined vertebral and proximal femoral (postcranial) bone mineral density in relation to tooth loss and attachment loss in a cross-sectional study of 135 postmenopausal women (age range 41-70 yr). Women had at least 10 teeth and no evidence of moderate or severe periodontal disease. Full-mouth attachment loss measurements were made using a pressure-sensitive probe, and bone density was determined by dual-energy X-ray absorptiometry. Attachment loss was correlated with tooth loss (number of remaining teeth, radiologically determined), but not with vertebral or proximal femur bone density. Multivariate analysis showed current smoking (p = 0.01), years since menopause (p = 0.02) and the interaction of age and current smoking (p < 0.01), to be statistically significant predictors of attachment loss in our study population.

Absorptiometry, Photon↗
PubMed1997

An intact N terminus is required for the anabolic action of parathyroid hormone on adult female rats.

Intermittent administration of parathyroid hormone (PTH) peptides increases bone density in animal and human models of osteoporosis. In vitro studies have demonstrated that PTH analogs lacking the first two amino acids can stimulate cell proliferation in certain cell systems, whereas fragments with an intact N terminus can be antimitogenic. We have tested whether the truncated PTH(3-38) fragment may be a better "anabolic analog" than PTH(1-38) by monitoring bone density and biomechanical properties of the femur in 6-month-old ovariectomized (OVX) rats. Either PTH fragment was administered subcutaneously (8 micrograms/100 g of body weight) 5 days/week, for 4 weeks, starting 1 week after surgery. During the entire study, untreated OVX rats lost 12.1 +/- 4.4% of their initial bone density. PTH(1-38) reversed the initial bone loss, leading to complete restoration of presurgery values after 4 weeks of treatment. Conversely, administration of PTH(3-38) resulted in 13.2 +/- 5.8% bone loss, while continuous estrogen infusion (10 micrograms/kg/day) prevented bone loss but did not reverse it. Sham-operated animals also experienced significant bone loss in the vehicle and PTH(3-38)-treated groups (-4.5 +/- 6.7%, and -7.6 +/- 2.8%, respectively), whereas a significant gain in bone density (+4.4 +/- 5.6%) was observed in the rats treated with PTH(1-38). A bone quality factor (index of strain energy loss) and the impact strength (resistance to fracture) were 25% and 44% lower in femurs explanted from OVX animals treated with either vehicle or PTH(3-38), compared with sham-operated animals. On the contrary, no difference was observed between OVX and control animals after treatment with PTH(1-38), indicating a preservation of the capacity to withstand mechanical stress. Thus, PTH(1-38) counteracts estrogen-dependent loss of mineral density and bone biomechanical properties and increases bone density in estrogen-replete animals. An intact N terminus sequence is necessary for this anabolic action of PTH.

Amino Acid Sequence↗
PubMed1996

Ipriflavone does not alter bone apatite crystal structure in adult male rats.

We have previously found that a short-term treatment with high doses of ipriflavone increased bone density and improved the biomechanical properties of adult male rat bones, without altering their mineral composition. To determine whether this effect can be associated with alterations of bone crystal structure, we have performed X-ray diffraction analysis of bones obtained from rats treated with ipriflavone at doses that were effective in inducing favorable changes on bone density and biomechanics. Eighteen-week-old male Sprague Dawley rats were treated by oral route with either ipriflavone (200 or 400 mg/kg/day), or its vehicle for 12 weeks. The treatment was well tolerated and body weight increased to the same extent in all animals. As a measure of bone crystallinity, we examined the (310) and (002) reflections of the X-ray diffraction patterns, corresponding to the directions perpendicular and parallel to the c-axis of the crystals, respectively. No major differences were observed between ipriflavone-treated and control animals for the broadening parameter beta(1/2) for (310) and (002) peaks, as well as for lattice parameters. Therefore, a 12-week treatment with ipriflavone at high doses does not induce significant modifications of bone "crystallinity." Thus, the positive effect of ipriflavone on bone mineral density appears to be associated with an increased apatite crystal formation rather than an increase of crystal size. These results provide further evidence for the safety and usefulness of ipriflavone in the treatment of osteoporotic syndromes.

Animals↗
PubMed1996

Endocrine and physical determinants of bone mass in late postmenopause.

To analyze the relative contribution of endocrine and physical factors to bone mineral density (BMD) in late menopause, we studied biochemical markers of bone turnover as well as sex and calciotropic hormones in 53 women (mean age 61 +/- 5.3 years), 5 to 23 years after natural menopause. BMD was measured at the lumbar spine and proximal femur by dual energy radiography. Stepwise regression analysis showed that age and PTH levels were the two major factors that significantly accounted for spinal BMD, with a final r2 = 0.27. Plasma androstenedione was the only other variable that contributed, albeit not significantly, to spine BMD increasing the r2 by 2%. Conversely, body mass was the main contributor to femoral BMD at all sites. While serum calcium and urinary hydroxyproline were significant determinants of neck BMD, urinary hydroxyproline and age provided significant source of variation for trochanteric BMD, and circulating FSH for BMD in the Ward's area. The final models gave r2 values of 0.35, 0.31, and 0.23, for neck, trochanter and Ward's areas, respectively. Thus, determinants of bone density differentially affect the vertebral and proximal femoral sites. While increasing age and PTH, probably reflecting a subclinical vitamin D deficiency, explain a decreased vertebral bone density, body mass appears to affect mostly the proximal femur. Circulating androgens play a secondary role. A persistently increased bone turnover state is conducive to lower bone density in late postmenopausal women.

Androstenedione↗
PubMed1995

Bone density in white Brazilian women: rapid loss at the time around the menopause.

Dual energy x-ray absorptiometry (DXA) was used to measure bone mineral density (BMD) of the lumbar spine and proximal femur (neck, Ward's triangle, and trochanter) in 417 normal women (aged 20-79) living in São Paulo, Brazil. Bone density decreased with age at all sites. At the spine, the greatest decrease occurred during the sixth decade, with an average 11.4% bone loss compared with the previous decade. Stratifying the subjects according to menopausal status revealed that the fastest bone loss occurred at the time around the menopause (ages 45-60) when the rate of bone loss (-0.66%/year) was almost twice as rapid as in postmenopausal women (-0.39%/year). Although significant linear rates of bone loss were detected in all proximal femur sites before the menopause, a menopause-dependent pattern was less evident than at the spine. Lifetime rates of bone loss at the appendicular skeleton were -0.43, -0.62, and -0.35%/year at the femoral neck, Ward's triangle, and trochanteric area, respectively. After the menopause, BMD declined with menopausal age at all sites, although the rate of bone loss was faster at the femoral neck (-0.62%/year) and Ward's triangle (-0.84%/year) than at the spine (-0.49%/year). The results are consistent with the notion that in women, the fastest bone loss occurs at the time around the menopause, most likely consequent to ovarian failure; and that faster rates of bone loss are detected at the proximal femur than at the lumbar spine in late postmenopausal women.

Absorptiometry, Photon↗
PubMed1995

Ipriflavone improves bone density and biomechanical properties of adult male rat bones.

To assess the potential impact of ipriflavone on the biomechanical properties and mineral composition of bone, we administered two doses (200 or 400 mg/kg bw) of the drug orally to adult male rats for 1 month. Bone biomechanics were evaluated by vibration damping, an index of strain energy loss, and impact strength (the amount of energy required to fracture after a single impact). At the higher dose, ipriflavone significantly decreased vibration damping of rat femurs by 23.0 +/- 9.8% compared with control, vehicle-treated animals, suggesting a higher capacity to withstand dynamic stress. This result was confirmed by the impact strength studies showing that a higher energy (49.6 +/- 21.3% above control) was required to fracture femurs of rat treated with 400 mg/kg bw ipriflavone. The high dose of ipriflavone increased bone mineral density, assessed by both volume displacement and ash analysis (4.2% and 2.5% above controls, respectively). The relative content of calcium, phosphorus, and magnesium in the ashes was not different among the treated and untreated groups, indicating that no gross abnormalities in mineral composition of bone occurred after ipriflavone administration. Similarly, there were no differences in serum calcium and magnesium levels between treated and control animals at the end of the study, whereas lower circulating phosphorus levels were detected in the latter. Ipriflavone treatment was not associated with significant changes in serum alkaline phosphatase nor type I collagen telopeptide levels, two markers of bone turnover. In summary, 1-month treatment with ipriflavone increased bone density and improved the biomechanical properties of adult rat male bones without altering mineral composition.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1995

Transfected connexin45 alters gap junction permeability in cells expressing endogenous connexin43.

Many cells express multiple connexins, the gap junction proteins that interconnect the cytosol of adjacent cells. Connexin43 (Cx43) channels allow intercellular transfer of Lucifer Yellow (LY, MW = 443 D), while connexin45 (Cx45) channels do not. We transfected full-length or truncated chicken Cx45 into a rat osteosarcoma cell line ROS-17/2.8, which expresses endogenous Cx43. Both forms of Cx45 were expressed at high levels and colocalized with Cx43 at plasma membrane junctions. Cells transfected with full-length Cx45 (ROS/Cx45) and cells transfected with Cx45 missing the 37 carboxyl-terminal amino acids (ROS/Cx45tr) showed 30-60% of the gap junctional conductance exhibited by ROS cells. Intercellular transfer of three negatively charged fluorescent reporter molecules was examined. In ROS cells, microinjected LY was transferred to an average of 11.2 cells/injected cell, while dye transfer between ROS/Cx45 cells was reduced to 3.9 transfer between ROS/Cx45 cells was reduced to 3.9 cells. In contrast, ROS/Cx45tr cells transferred LY to > 20 cells. Transfer of calcein (MW = 623 D) was also reduced by approximately 50% in ROS/Cx45 cells, but passage of hydroxycoumarin carboxylic acid (HCCA; MW = 206 D) was only reduced by 35% as compared to ROS cells. Thus, introduction of Cx45 altered intercellular coupling between cells expressing Cx43, most likely the result of direct interaction between Cx43 and Cx45. Transfection of Cx45tr and Cx45 had different effects in ROS cells, consistent with a role of the carboxyl-terminal domain of Cx45 in determining gap junction permeability or interactions between connexins. These data suggest that coexpression of multiple connexins may enable cells to achieve forms of intercellular communication that cannot be attained by expression of a single connexin.

Animals↗
PubMed1995

Estrogen action on the bone mass of postmenopausal women is dependent on body mass and initial bone density.

Recent evidence suggests that estrogen replacement therapy (ERT) may be effective in preventing bone loss even in late postmenopausal women. We analyzed the role of age and other factors as determinants of ERT action on vertebral bone density (VBD) in 73 consecutive Caucasian postmenopausal women treated for 1 yr or longer. A group of 44 women who received calcium supplements only were analyzed as controls. VBD was measured every 6 months by dual energy x-ray absorptiometry, and yearly rates of change were calculated by linear regression for each subject. VBD increased in the estrogen-treated group (+17.32 +/- 2.84 mg/cm2.yr; 2.42 +/- 0.37%/yr) and did not significantly change in untreated subjects (-4.08 +/- 3.68 mg/cm2/yr; -0.60 +/- 0.58%/yr). Women older than 60 yr experienced greater, although not significant, increments compared to younger subjects (+3.23 +/- 4.03% vs. +1.42 +/- 3.00%/yr), as did women more than 10 yr postmenopausal compared to patients within 10 yr after the menopause (+3.38 +/- 4.11% vs. +1.19 +/- 2.70%/yr). Rates of VBD change were positively correlated with age (r = 0.29; P = 0.014), years since menopause (r = 0.33; P = 0.005), and body mass index (BMI; r = 0.35; P = 0.003) and negatively with estimated initial VBD (r = -0.23; P = 0.05). However, only the relationships between bone density changes and BMI (r = 0.33; P < 0.01) and estimated initial VBD (r = -0.26; P < 0.05) held in a partial correlation analysis. BMI and estimated initial VBD were the only significant predictive factors for response to ERT (r2 = 21%) in a multivariate regression model. Therefore, the response to ERT depends mostly on BMI and initial VBD. Women with large body frames and those with lower initial VBD respond better to estrogen than slender women with higher bone mass.

Age Factors↗
PubMed1995

Activation of the Ca2+ message system by parathyroid hormone is dependent on the cell cycle.

Putative osteoblastic UMR 106-01 cells exhibit heterogeneous intracellular calcium [Ca2+]i responses to parathyroid hormone (PTH). To determine whether this phenomenon is secondary to cell cycle asynchrony, UMR 106-01 cultures were synchronized at the G1/S boundary using a sequential thymidine-aphidicolin treatment. Five hours after release from the block > 80% of the cells are in S phase, while nontreated confluent cultures are in G1. Using video image analysis of single cells loaded with fura-2, PTH (10-(7) M) induced transient increases in [Ca2+]i preferentially in cells in S phase, with 82% response frequency whereas cells in G1 phase responded poorly to PTH with only 10% response frequency. In contrast, cell response to fetal calf serum was more frequent in G1 than in S phase. Pretreatment with La3+, nifedipine or pertussis toxin reduced both the frequency and amplitude of the PTH response in S phase to values comparable to those observed in cells in G1 phase. There was no significant difference in inositol trisphosphate generated by PTH stimulation in either phase. Thus, the heterogeneous osteoblastic [Ca2+]i responsive to PTH is cell cycle-dependent with the change in the G1 to the S phase mode of response dependent on active coupling between the PTH receptor and a Ca2+ channel via a pertussis toxin-sensitive G protein.

Calcium↗
PubMed1995

Evaluation of bone resorption: a common problem during impaired mobility.

Osteoporosis, the result of an imbalance between bone resorption and bone formation, is a potential problem for the individual with a spinal cord injury because of the immobility commonly associated with this impairment. This study was performed to determine the diagnostic value of a new assay for urinary Pyridinium crosslink (UPyr). Assays were performed on 62 first morning voided and 50 24-hour urine specimens from clients in a bone health clinic. Higher than normal levels of UPyr were observed in females with osteoporosis. UPyr correlated well with urinary hydroxyproline (r = 0.429, p = 0.005; conversely, there was an inverse relationship between bone density and UPyr (r = -0.489, p = 0.01), positive correlation (r = 0.43, p = 0.011) between the 24-hour UPyr and a serum marker of bone resorption. The study confirms that UPyr has the ability to identify states of high bone resorption. This assay should be a welcome addition to the bone health assessment of individuals with risk factors such as impaired physical mobility.

Adult↗
PubMed1994

Ligand binding to monocyte alpha 5 beta 1 integrin activates the alpha 2 beta 1 receptor via the alpha 5 subunit cytoplasmic domain and protein kinase C.

Regulation of the functional status of integrin receptors plays a critical role in inflammation and tissue remodeling, as it affects cell adherence and cytokine secretion. We have previously shown that in monocytes the binding of collagen to the alpha 2 beta 1 integrin induces the release of IL-1, an event that is potentiated by binding of fibronectin (Fn) to the alpha 5 beta 1 integrin. In this study, we have investigated the mechanisms leading to this phenomenon. Fn binding to alpha 5 beta 1 induced intracellular signals which increased the alpha 2 beta 1-dependent adhesiveness of monocytes to collagen without modifications of alpha 2 beta 1 expression. By using Abs against the intracellular region of the alpha 5 subunit of the alpha 5 beta 1 receptor, and specific inhibitors of protein kinase C (PKC), we found that the potentiation effect of Fn on monocyte IL-1 production and their adherence to collagen was dependent on an intact alpha 5 subunit cytoplasmic domain, and required PKC activation. Although the alpha 2 beta 1 could be activated by several intracellular second messengers, including protein kinase A and intracellular calcium, the potentiating effect of Fn was mediated only by PKC. These data provide an example of a novel regulatory mechanism: potentiation of beta 1 integrin-mediated events as a result of ligand binding to another integrin of the same class. They also show that the intracellular region of alpha 5 beta 1 plays a critical role in transducing signals generated by ligand binding to alpha 5 beta 1.

Calcium↗