Differential regulation of communication by retinoic acid in homologous and heterologous junctions between normal and transformed cells.

The permeability of junctions between cells of the same type (homologous junctions) is greatly increased by retinoic acid (10(-9)-10(-8) M), a probable morphogen, and this responsiveness is shared by a variety of normal and transformed cell types (Mehta, P.P., J.S. Bertram, and W.R. Loewenstein. 1989. J. Cell Biol. 108:1053-1065). Here we report that the heterologous junctions between the normal and transformed cells respond in the opposite direction; their permeability is reduced by retinoic acid (greater than or equal to 10(-9) M) and its benzoic acid derivative tetrahydrotetramethylnaphthalenylpropenylbenzoic acid (greater than or equal to 10(-11) M). The opposite responses of the two classes of junction are shown to be concurrent; in cocultures of normal 10T1/2 cells and their methylcholanthrene-transformed counterparts, the permeability of the heterologous junctions, which is lower than that of the homologous junctions to start with, falls (within 20 h of retinoid application), at the same time that the permeability of the homologous junctions rises in both cell types. Such a counter-regulation requires a minimum of three degrees of cellular differentiation. A model is proposed in which the differentiations reside in a trio of junctional channel protein. The principle of the model may have wide applications in the regulation of intercellular communication at tissue boundaries, including embryonic ones.

The actions of retinoids on cellular growth correlate with their actions on gap junctional communication.

Retinoic acid (a possible morphogen), its biological precursor retinol, and certain synthetic derivatives of retinol profoundly change junctional intercellular communication and growth (saturation density) in 10T 1/2 and 3T3 cells and in their transformed counterparts. The changes correlate: growth decreases as the steady-state junctional permeability rises, and growth increases as that permeability falls. Retinoic acid and retinol exert quite different steady-state actions on communication at noncytotoxic concentrations in the normal cells: retinoic acid inhibits communication at 10(-10)-10(-9) M and enhances at 10(-9)-10(-7) M, whereas retinol only enhances (10(-8)-10(-6) M). In v-mos-transformed cells the enhancement is altogether lacking. But regardless of the retinoid or cell type, all growth responses show essentially the same dependence on junctional permeability. This is the expected behavior if the cell-to-cell channels of gap junctions disseminate growth-regulating signals through cell populations.

Neural differentiation, NCAM-mediated adhesion, and gap junctional communication in neuroectoderm. A study in vitro.

We studied the development of NCAM and gap junctional communication, and their mutual relationship in chick neuroectoderm in vitro. Expression of NCAM, as detected by monoclonal and polyclonal antibodies, and development of junctional communication, as detected by extensive cell-to-cell transfer of 400-500-D fluorescent tracers, occurred in cultures from stage-2 embryos onward. Both expressions presumably required primary induction. The differentiating cells formed discrete fields of expression on the second to third day in culture, with the NCAM fields coinciding with the junctional communication fields delineated by the tracers. Other neural differentiations developed in the following order: tetanus toxin receptors, neurofilament protein, and neurite outgrowth. Chronic treatment with antibody Fab fragments against NCAM interfered with the development of communication, suggesting that NCAM-mediated adhesion promotes formation of cell-to-cell channels. Temperature-sensitive mutant Rous sarcoma virus blocked (reversibly) communication and the subsequent development of neurofilament protein and neurites, but expression of NCAM continued.

IFN-gamma-induced expression of MUC4 in pancreatic cancer cells is mediated by STAT-1 upregulation: a novel mechanism for IFN-gamma response.

MUC4 is a transmembrane mucin, which is aberrantly expressed in pancreatic adenocarcinoma with no detectable expression in the normal pancreas. Here, we present a novel mechanism of IFN-gamma-induced expression of MUC4 in pancreatic cancer cells. Our studies highlight the upregulation of STAT-1 as a basis for MUC4 induction and demonstrate that its activation and upregulation by IFN-gamma are two distinct, albeit temporally integrated, signalling events that drive the selective induction of IRF-1 and MUC4, respectively, within a single cell system. The profile of interferon regulatory factor (IRF)-1 gene induction by IFN-gamma is consistent with its rapid transactivation by phospho-Y701-STAT-1. In contrast, the induction of the MUC4 mucin gene expression is relatively delayed, and occurs only in response to an increase in STAT-1 expression. A progressive binding of STAT-1 to various gamma-interferon-activated sequences (GAS) in the MUC4 promoter is observed in chromatin immunoprecipitation assay, indicating its direct association. Stimulation of STAT-1 expression by double-stranded polynucleotides or ectopic expression is shown to induce MUC4 expression, without Y701 phosphorylation of STAT-1. This effect is abrogated by short interfering RNA (siRNA)-mediated inhibition of STAT-1 expression, supporting further the relevance of STAT-1 in MUC4 regulation. In conclusion, our findings identify a novel mechanism for MUC4 regulation in pancreatic cancer cells and unfold new perspectives on the foundation of IFN-gamma-dependent gene regulation.

Transcription of the gene for the gap junctional protein connexin43 and expression of functional cell-to-cell channels are regulated by cAMP.

We investigated the mechanism by which cyclic AMP (cAMP) induces gap junctional communication via cell-to-cell channels in a communication-deficient rat Morris hepatoma cell line. We found that under basal conditions, the cells transcribe cx43 at a low level but do not transcribe cx26 or cx32. Elevation of intracellular cAMP, which induced communication, increased cx43 mRNA 15- to 40-fold and the rate of cx43 transcription 6-fold. Cx43 protein was detected by immunostaining in junctions of only those cells in which communication had been induced. We found the regulation by cAMP also in other cell lines; namely, in those with a low basal level of cx43 mRNA.

Prostate cancer progression, metastasis, and gene expression in transgenic mice.

We previously reported that a transgenic mouse line containing the fetal globin promoter linked to the SV40 T antigen (T Ag) viral oncogene (Ggamma/T-15) resulted in prostate tumors. In this study, we further explored tumor origin, frequency, invasiveness, androgen sensitivity, and gene expression pattern. T Ag was detected in adult but not fetal and neonatal prostates, suggesting a role for androgens in tumor progression. However, castration shortly after prostate morphogenesis did not prevent tumor development, suggesting an androgen-independent phenotype. Tumors originated within ventral or dorsal prostate lobes and involved intraepithelial neoplasia, rapid growth in the pelvic region, and metastasis to lymph nodes and distant sites. In addition, the primary cancers could be propagated in nude mice or nontransgenic mice. Seventy-five percent of hemizygous and 100% of homozygous transgenic males developed prostate tumors, suggesting a T Ag dosage effect. Biochemical characterization of advanced tumors revealed markers of both neuroendocrine and epithelial phenotypes; markers of terminal differentiation are lost early in tumorigenesis. Tumor suppressor genes (p53 and Rb), normally bound to T Ag, were up-regulated; bcl-2 proto-oncogene, which prevents apoptosis, was slightly up-regulated. Myc, a stimulus to cell cycle progression, was unchanged. We propose the Ggamma/T-15 transgenic line as a model of highly aggressive androgen-independent metastatic prostate carcinoma with features similar to end-stage prostate cancer in humans.

Hypocholesterolemic action of 1-ethoxysilatrane.

Intraperitoneal administration of the organosilicon compound 1-ethoxysilatrane to the rat caused a 25% decrease in the concentration of cholesterol in serum without affecting that of triacylglycerols. The specific activity of 3-hydroxy-3-methylglutaryl CoA reductase, the rate-limiting enzyme in cholesterol biosynthesis, was depressed in hepatic microsomes of silatrane-treated animals.

Hormonal regulation of intercellular communication: parathyroid hormone increases connexin 43 gene expression and gap-junctional communication in osteoblastic cells.

The presence of gap junctions between osteoblastic cells has been previously reported. For this study we used the rat osteosarcoma cell line UMR 106, which expresses the osteoblastic phenotype, as a model to characterize further the nature, physiology, and regulation of gap junctions. Northern blot analysis identified a 3.0-kilobase RNA species corresponding to the gap junction protein connexin 43. The presence of two other connexin RNA species (26 and 32) could not be detected by this method in these cells. The identified connexin RNA was amplified by reverse transcription coupled to polymerase chain reaction; the sequence of the amplified product appears identical to the sequence of a cloned rat heart connexin 43 gene. After treatment with PTH, forskolin, and 8-Br-cAMP (a cAMP analog), the levels of connexin 43 RNA in UMR 106 cells increased. Further evidence for the role of PTH and cAMP in the physiology of gap junctions in these cells was obtained with Lucifer yellow dye transfer experiments. Gap-junctional intercellular communication increased in response to PTH and forskolin (an inducer of adenylate cyclase activity). Expression of connexin 43 RNA increased severalfold in response to PTH in a concentration- and time-dependent fashion. Connexin 43 RNA and its PTH-mediated stimulation were also observed in several other osteoblastic cell lines. The roles of PTH and forskolin in regulating the physiological state of gap junctions were confirmed in primary cultures of rat calvaria osteoblasts.

Facilitation of gap-junctional communication and gap-junction formation in mammalian cells by inhibition of glycosylation.

The effect of inhibition of glycosylation on basal and cAMP-induced homologous and heterologous gap-junctional communication was studied in various normal and transformed cell lines that express mRNA and protein for the gap-junction-forming gene, connexin43. In communication-incompetent Morris hepatoma cells, inhibition of glycosylation alone did not induce junctional communication, but enhanced cAMP-induced junctional communication severalfold. This enhancement correlated with the presence of more gap junctions at the membrane appositions, but not with an increase in connexin43 mRNA or protein in these cells. In several other normal and transformed cell lines, inhibition of glycosylation enhanced both basal as well as cAMP-induced junctional communication. Furthermore, both basal and cAMP-induced heterologous junctional communication between nontransformed RL-CL9 and several other nontransformed and transformed cells was also enhanced when glycosylation was inhibited. Our data suggest that the formation of gap junctions between cells of the same type or different types is subject to local constraints imposed by the oligosaccharide moieties of the glycoproteins of the plasma membranes of the gap-junction-forming cells and that inhibition of glycosylation abrogates such constraints. Our findings thus suggest a new basis for the communication deficiency observed in several types of transformed cells and between transformed and normal cells.

Botulinum neurotoxins serotypes A and E cleave SNAP-25 at distinct COOH-terminal peptide bonds.

SNAP-25, a membrane-associated protein of the nerve terminal, is specifically cleaved by botulinum neurotoxins serotypes A and E, which cause human and animal botulism by blocking neurotransmitter release at the neuromuscular junction. Here we show that these two metallo-endopeptidase toxins cleave SNAP-25 at two distinct carboxyl-terminal sites. Serotype A catalyses the hydrolysis of the Gln197-Arg198 peptide bond, while serotype E cleaves the Arg180-Ile181 peptide lineage. These results indicate that the carboxyl-terminal region of SNAP-25 plays a crucial role in the multi-protein complex that mediates vesicle docking and fusion at the nerve terminal.

Phosphorylation of high- and low-molecular-mass atrial natriuretic peptide analogs by cyclic AMP-dependent protein kinase.

Synthetic high- and low-molecular-mass atrial peptides were phosphorylated in vitro by cyclic AMP-dependent protein kinase and [32P]ATP. From a series of atrial peptide analogs, it was deduced that the amino acid sequence, Arg101-Ser104 of atriopeptin was required for optimal phosphorylation. Phosphorylated AP(99-126) was less potent than the parent atriopeptin in vasorelaxant activity and receptor-binding properties. These results indicate that the presence of a phosphate group at the N-terminus of AP(99-126) decreases the interaction of the peptide with its receptor and, as a consequence, decreases bioactivity. These observations are in contrast to those of Rittenhouse et al. [(1986) J. Biol. Chem. 261, 7607-7610] who reported that phosphorylation of AP(101-126) enhanced the stimulation of Na/K/Cl cotransport in cultured vascular smooth muscle cells.

Conformationally constrained [p-(omega-aminoalkyl)phenacetyl]-L-seryl-L-lysyl dipeptide amides as potent peptidomimetic inhibitors of Candida albicans and human myristoyl-CoA:protein N-myristoyl transferase.

MyristoylCoA:protein N-myristoyltransferase (NMT) covalently attaches the 14-carbon saturated fatty acid myristate, via an amide bond, to the N-terminal glycine residues of a variety of cellular proteins. Genetic studies have shown that NMT is essential for the viability of the principal fungal pathogens which cause systemic infection in immunosuppressed humans and hence is a target for development of fungicidal drugs. We have generated a class of potent peptidomimetic inhibitors of the NMT from one such fungal pathogen, Candida albicans. The N-terminal tetrapeptide from a substrate analog inhibitor, ALYASKL-NH2, was replaced with an omega-aminoalkanoyl moiety having an optimal 11-carbon chain for inhibition (11-aminoundecanoyl-SKL-NH2, 3a, IC50 = 1.2 +/- 0.14 microM). A series of replacements for the C-terminal Leu established that residues containing a lipophilic side chain were most effective, with cyclohexylalanine having the greatest potency (3g, IC50 = 0.36 +/- 0.06 microM). Removal of the carboxamide moiety led to a metabolically stable dipeptide inhibitor containing an N-(cyclohexylethyl)lysinamide (17e, IC50 = 0.11 +/- 0.03 microM). Partial rigidification of the flexible aminoundecanoyl chain produced the dipeptide p-(omega-aminohexyl)phenacetyl-L-seryl-L-lysyl-N-(cyclohexyleth yl)amide (26b, IC50 = 0.11 +/- 0.04 microM). Subsequent incorporation of an alpha-methyl substituent into 26b provided the dipeptide analog [2-[p-(omega-aminohexyl)phenyl]propionyl]-L-seryl-L-lysyl-N-(cyclohex ylethyl)amide, a very potent inhibitor (48, IC50 = 0.043 +/- 0.006 microM), which retained the three essential elements required for recognition by the acyl transferase's peptide binding site.

Retrovirally mediated gene transfer in a skin equivalent model of chronic wounds.

Given that treatment for chronic wounds is unsatisfactory, it is likely that gene therapy may be tested as a therapeutic modality in this difficult clinical problem. Actively proliferating cells in wounds are also a good target for retroviral transduction, an increasingly useful method for gene therapy. However, it is unclear how gene therapy may best be used in chronic wounds, and experimental models are urgently needed to study and manipulate gene transfer in the context of chronic wounds. In this report, partial- and full-thickness wounds were made in vitro in a human living skin equivalent (LSE) consisting of fully differentiated keratinocytes layered over a collagen matrix seeded with fibroblasts. To mimic a chronic wound situation, we used tissue culture conditions which, as in a chronic wound, allowed fibroblast but not keratinocyte proliferation or migration. The wounded LSE was then placed over a transduced cell line (PA317) which produced a replication defective retrovirus containing as a histological marker the bacterial beta galactosidase gene. Using this close and direct exposure to the virus-producing cell line, distinct staining for beta-galactosidase was observed in partial-thickness wounds, and was limited to fibroblasts away from the upper site of injury and immediately overlying the retrovirus-producing cell monolayer. Expression of beta-galactosidase was uniformly present at the wound edges and along the base of the entire partial thickness wound. These studies demonstrate that, in in vivo conditions mimicking a chronic wound, an intimate apposition of the injured LSE with the virus-producing cell line is needed for gene transfer. Using this in vitro model system, gene transfer protocols may be optimized prior to beginning in vivo studies in chronic wounds.

Atriopeptin regulation and renal function in conscious spontaneously hypertensive rats.

We examined the interaction of a non-guanylate cyclase-linked atriopeptin (AP) binding site ligand, SC-46542 (des[Phe106,Gly107,Ala115,Gln116]AP-(103-126], and an endopeptidase 24.11 inhibitor, thiorphan, on mean arterial pressure, urinary sodium excretion, urinary cyclic guanosine monophosphate (cGMP) excretion, plasma cGMP concentration, and plasma AP immunoreactivity (ir) in conscious spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Compared to vehicle control rats, coadministration of SC-46542 and thiorphan increased urinary sodium excretion in SHR from 2.1 +/- 0.3 to 11.6 +/- 0.7 microEq/min/100 g body weight and in WKY from 1.6 +/- 0.4 to 4.4 +/- 0.4 microEq/min/100 g body weight, and increased urinary cGMP excretion in SHR from 2.7 +/- 0.5 to 79.0 +/- 17.5 pmol/min/100 g body weight and in WKY from 7.0 +/- 3.0 to 72.4 +/- 10.6 pmol/min/100 g body weight. The change in urinary sodium excretion was greater in SHR than WKY. The coadministration of SC-46542 and thiorphan had greater effects on urinary sodium excretion and urinary cGMP excretion than administration of either compound alone. Coadministration of thiorphan and SC-46542 had no effect on glomerular filtration rate or plasma cGMP concentration, suggesting that the urinary cGMP excretion response was nephrogenous. Compared to vehicle control rats, plasma APir was increased during coadministration of SC-46542 and thiorphan in both SHR (998 +/- 76 v 5.10 +/- 116 pg/mL) and WKY (775 +/- 36 v 414 +/- 36 pg/mL).(ABSTRACT TRUNCATED AT 250 WORDS)

Recent advances in cancer stem/progenitor cell research: therapeutic implications for overcoming resistance to the most aggressive cancers.

Overcoming intrinsic and acquired resistance of cancer stem/progenitor cells to current clinical treatments represents a major challenge in treating and curing the most aggressive and metastatic cancers. This review summarizes recent advances in our understanding of the cellular origin and molecular mechanisms at the basis of cancer initiation and progression as well as the heterogeneity of cancers arising from the malignant transformation of adult stem/progenitor cells. We describe the critical functions provided by several growth factor cascades, including epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor (PDGFR), stem cell factor (SCF) receptor (KIT), hedgehog and Wnt/beta-catenin signalling pathways that are frequently activated in cancer progenitor cells and are involved in their sustained growth, survival, invasion and drug resistance. Of therapeutic interest, we also discuss recent progress in the development of new drug combinations to treat the highly aggressive and metastatic cancers including refractory/relapsed leukaemias, melanoma and head and neck, brain, lung, breast, ovary, prostate, pancreas and gastrointestinal cancers which remain incurable in the clinics. The emphasis is on new therapeutic strategies consisting of molecular targeting of distinct oncogenic signalling elements activated in the cancer progenitor cells and their local microenvironment during cancer progression. These new targeted therapies should improve the efficacy of current therapeutic treatments against aggressive cancers, and thereby preventing disease relapse and enhancing patient survival.

Gap-junction protein gene suppresses tumorigenicity.

Prompted by the notion that the membrane channels in gap junctions conduct growth-regulating signals from cell to cell, we transferred the alpha 1 gene for the channel protein (connexin43) of rat heart to tumorigenic mouse MCA-10 cells. Upon incorporation into the cell genome, this exogenous gene was expressed, resulting in functional channels and normal growth regulation: cell-cell communication, determined with a channel-permeant 400-dalton fluorescent tracer, was increased and tumorigenicity, determined in nude mice, was suppressed.

Inhibition of glycosylation induces formation of open connexin-43 cell-to-cell channels and phosphorylation and triton X-100 insolubility of connexin-43.

We transfected the cDNA for the cell-to-cell channel protein connexin-43 (Cx43) into Morris hepatoma H5123 cells, which express little Cx43 and lack gap junctional communication (open cell-to-cell channels). We found that cells overexpressing Cx43 nonetheless lacked open cell-to-cell channels, but that inhibition of glycosylation by tunicamycin induced open channels in these cells. Tunicamycin also induced biochemical changes in Cx43 protein; the level increased, and a considerable fraction became phosphorylated and Triton X-100 insoluble, in contrast to untreated cells where Cx43 was non-phosphorylated and Triton X-100 soluble. Although tunicamycin caused the formation of open channels, channels were not found aggregated into gap junctional plaques, as they are when they have been induced by elevation of intracellular cAMP. The results suggest that although Cx43 itself is not glycosylated, other glycosylated proteins influence Cx43 posttranslational modification and the formation of Cx43 cell-to-cell channels.