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S D Chan

Publications and source records attributed to S D Chan.

9 recordsLinked to original sources
PubMed1992

Two homologs of the Drosophila polarity gene frizzled (fz) are widely expressed in mammalian tissues.

The frizzled (fz) locus of Drosophila encodes a protein (Fz) with a seven-transmembrane-domain profile characteristic of G-protein-coupled receptors. In Drosophila, genetic evidence suggests that Fz functions to transmit and transduce polarity signals in epidermal cells during hair and bristle development. We have isolated from a UMR 106 rat osteosarcoma cell library a cDNA (fz-1) encoding a predicted 641-residue protein (Fz-1) with 46% homology with Drosophila Fz. We also identified a second cDNA (fz-2) encoding a protein (Fz-2) of 570 amino acids that is 80% homologous with Fz-1, with divergence most evident in the extracellular domains. Southern blots of rat genomic DNA indicated that fz-1 and fz-2 represent distinct genes. Northern analysis revealed the presence of a single fz-1 mRNA (4.7 kilobases) and two fz-2 mRNAs (2.5 and 4.5 kilobases) in rat tissues. The fz-1 and fz-2 genes are widely expressed in rat tissues with the highest steady-state levels of mRNA in kidney, liver, heart, uterus, and ovary. fz-1 and -2 mRNA levels were greater in neonatal than in corresponding adult tissues. Treatment of UMR 106 cells with bone resorbing agents including parathyroid hormone, epidermal growth factor, and 1,25-dihydroxyvitamin D3 produced increases in fz-1 and -2 mRNA levels. We suggest that hormonal induction of Fz proteins in osteoblasts serves to promote intercellular signaling required for functional responses such as increased bone resorption. Fz-1 and Fz-2 may represent products of a gene family whose members serve as transducers or intercellular transmitters of signals required for normal morphogenesis and/or differentiated function in diverse tissues.

Amino Acid Sequence↗
PubMed1991

Chicken parathyroid hormone-related protein and its expression during embryologic development.

A parathyroid hormone-related protein (PTHrP) is the probable cause of humoral hypercalcemia in malignancy, but its normal physiologic role remains unknown. Since current evidence suggests that PTHrP may have a role in embryonic development, we cloned a genomic fragment that encodes chicken PTHrP (cPTHrP) and studied the expression of PTHrP in developing chick embryos. Blot hybridization of chicken genomic DNA with a cPTHrP genomic DNA probe showed a single band, suggesting that a single-copy gene encodes cPTHrP. By screening a chicken genomic library with the human probe an open reading frame was identified that corresponds to the human PTHrP (hPTHrP) exon IV. Compared to the human sequence the 5' splice junction is highly conserved and the two predicted propeptide residues are identical. The sequence predicts a mature peptide of 139 amino acids; all of the first 21 and 94 of the first 112, but only 8 of the final 27 residues of cPTHrP are identical to the human sequence. The structural features required for PTH receptor binding and activation are highly conserved between chicken and hPTHrP. Poly(A)-enriched RNA from 3-15 day chicken embryos was surveyed by hybridization to the chicken probe. A hybridizing band of 1.45 kb was found in tissues derived from all three germ layers, including brain, heart, lung, liver, gizzard, intestine, chorioallantoic membrane, yolk sac, and skeletal muscle. An additional 1.2 kb hybridizing band was found in some tissues. The conservation of the PTHrP sequence between chicken and mammals supports the view that PTHrP has an important physiologic role.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1990

Transcriptional activation of Gs alpha expression by retinoic acid and parathyroid hormone-related protein in F9 teratocarcinoma cells.

Cyclic AMP is known to enhance retinoic acid-induced differentiation of F9 mouse teratocarcinoma cells to parietal endoderm. Recently, we showed that a parathyroid hormone-related protein (PTHrP), by activating adenylate cyclase, can substitute for exogenous cAMP in promoting retinoic acid-induced differentiation of F9 cells. However, the mechanisms by which endogenous cAMP levels are regulated during F9 differentiation are poorly defined. We therefore assessed whether Gs alpha, a subunit of the stimulatory coupling protein of adenylate cyclase, is induced during this process. Treatment of F9 cells with retinoic acid (1 microM) for 5 days resulted in a 20-fold increase in steady-state levels of a 2.0-kilobase Gs alpha mRNA. This was accompanied by an increase in the expression of 52- and 45-kDa Gs alpha polypeptides. Gs alpha mRNA increases within 24 h of exposure to retinoic acid, whereas the expression of alpha 1 (IV) collagen, a marker for F9 differentiation, did not increase until 48 h of treatment. In the presence of retinoic acid, exogenous human PTHrP-(1-34)-amide (20 nM) produced a further 2-fold increase in Gs alpha mRNA. These effects of retinoic acid and PTHrP were exerted largely if not entirely at the level of Gs alpha gene transcription, as assessed by nuclear run-on assay. Bt2cAMP (1 mM) did not reproduce the stimulatory effects of PTHrP on Gs alpha transcription, mRNA, or protein. These data demonstrate that a marked increase in Gs alpha expression accompanies F9 differentiation induced by retinoic acid and PTHrP, and that the regulation is predominantly transcriptional. The resulting increase in adenylate cyclase responsiveness to PTHrP and perhaps other ligands may be a critical component of the differentiation process. The effect of PTHrP on the expression of Gs alpha appears to be mediated by signals other than cAMP.

Animals↗
PubMed1990

The gene for the alpha 2 chain of the human fibrillar collagen type XI (COL11A2) assigned to the short arm of chromosome 6.

A cosmid clone (CosHcol.11) containing the alpha 2(XI) collagen gene (COL11A2) has been isolated. The gene contains conserved DNA and amino-acid sequences characteristic of fibril forming collagen, which is in accordance with the classification of type XI collagen as a fibrillar collagen. The genomic clone containing the alpha 2(XI) gene has been used as probe in the Southern blot analysis of DNA from a panel of human/hamster somatic cell hybrids containing different numbers and combinations of human chromosomes. Synteny analysis revealed that only chromosome 6 showed complete concordant segregation with COL11A2. Furthermore, the gene was regionally mapped to the short arm of chromosome 6 by using a hybrid which contained only the long arm of the chromosome.

Blotting, Southern↗
PubMed1990

Expression of a parathyroid hormone-like protein and its receptor during differentiation of embryonal carcinoma cells.

Differentiation of mouse embryonal carcinoma cells to the parietal endoderm phenotype is associated with expression of PTH-responsive adenylate cyclase. A PTH-like protein (PLP), which binds to PTH receptors and activates adenylate cyclase in classical PTH target cells was recently isolated and cloned. We assessed whether the parietal endoderm phenotype is associated with the expression of PLP or its receptor. A 1.4-kilobase PLP transcript was detected in the mouse parietal endoderm cell line PYS-2. No hybridizing transcripts were evident in undifferentiated mouse embryonal carcinoma cells PSA-1 or F9. However, differentiation of these cells to parietal endoderm, either spontaneously (PSA-1) or by treatment with retinoic acid and dibutyryl cAMP (F9), resulted in expression of the 1.4-kilobase PLP message. Undifferentiated F9 cells displayed negligible specific binding of [125I]PLP-(1-34)amide. When F9 cells were induced to differentiate to parietal endoderm, specific binding sites for [125I]PLP-(1-34)amide were expressed in parallel with PLP-responsive adenylate cyclase. These receptors, like those in classical PTH target tissues, displayed identical affinity (Kd = 5.2 nM) for bPTH-(1-34) and hPLP-(1-34)amide; with binding capacity (Bmax) of 6.6 x 10(4) sites/cell. In the presence of retinoic acid, exogenous PLP substituted for dibutyryl cAMP in a concentration-dependent fashion in promoting the differentiation of F9 cells to parietal endoderm. Thus, both PLP mRNA and PLP receptors coupled to adenylate cyclase are expressed during the differentiation of mouse embryonal carcinoma cells. Increased cAMP levels produced by autocrine stimulation of PLP receptors by PLP may contribute to differentiation of embryonal carcinoma cells into parietal endoderm.

Adenylyl Cyclases↗
PubMed1989

The human alpha 2(XI) collagen (COL11A2) chain. Molecular cloning of cDNA and genomic DNA reveals characteristics of a fibrillar collagen with differences in genomic organization.

We have isolated three overlapping cDNA clones encoding the pro alpha 2(XI) collagen chain from a human chondrocyte cDNA library. Together, the cDNAs code for 257 uninterrupted Gly-X-Y triplets (almost 80% of the triple helical domain) and about 200 amino acid residues of the carboxyl telopeptide and carboxyl propeptide. The identification of the clones as pro alpha 2(XI) cDNAs was based on the complete identity between the amino acid sequences of three tryptic peptides derived from human alpha 2(XI) collagen and the cDNA-derived sequence. We have also sequenced six exons within a human genomic alpha 2(XI) cosmid clone. This sequence shows that although type XI collagen belongs to the fibril-forming class of collagens, there are substantial differences in exon sizes at the 3' end of the gene when comparing the alpha 2(XI) gene with those of human types I, II, and III collagens. Finally, pro alpha 2(XI) cDNA has been used as a probe to determine the location of the gene by in situ hybridization of chromosome spreads. The results demonstrate that the gene is located close to the region p212 on chromosome 6. Northern blot analysis shows that the gene is expressed in cartilage but not in adult liver, skin, and tendon.

Amino Acid Sequence↗