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L Piché

Publications and source records attributed to L Piché.

8 recordsLinked to original sources
PubMed1996

Role of bcl-X(L) in the control of apoptosis in murine myeloma cells.

The development of an increasing number of tumors has been shown to involve the deregulation of not only cell proliferation but also normal cell death by apoptosis. Expression of the bcl-2 proto-oncogene has been shown to inhibit the apoptotic cell death of many types of cells. Recent work also has revealed the existence of several bcl-2-related genes that also can inhibit (e.g., bcl-X(L) and Mcl-1) or activate (e.g., bax, bcl-X(s), bag, and bad) apoptosis in several systems. Myelomas are antibody-secreting tumor cells derived from terminally differentiated B lymphocytes, and previous work from our laboratory showed that murine SP2/0 myeloma cells and derived B-cell hybridomas were highly sensitive to apoptosis induction by a block of gene expression (cycloheximide). Additional work revealed that a related murine myeloma cell line, P3X63Ag8.653, was resistant to apoptosis induction in similar conditions. To understand the genetic basis of this differential susceptibility, we examined the expression of apoptosis-related genes in these cell lines. Northern blot experiments showed no significant difference in the expression of myc and bax apoptosis-promoting genes in susceptible (SP2/0 and D5) and resistant (P3X63) cell lines. Also, no significant expression of the bcl-2 gene could be detected in these cell lines. However, a much higher expression level of bcl-X(L) mRNA was observed in apoptosis-resistant P3X63Ag8.653 cells. The role of bcl-X(L) was supported by the finding that expression of bcl-X(L) cDNA in transfected, apoptosis-sensitive D5 cells increased the viability of these cells greatly and reduced DNA fragmentation following apoptosis induction. Significant bcl-X(L) but not bcl-2 expression was also detected in three other murine myeloma cell lines (MOPC 315, RPC 5.4, and J558) derived from different plasmacytoma tumors. These results indicate a predominant role of bcl-X(L) in preventing apoptosis in myeloma cells and suggest that the expression of bcl-2 or bcl-X(L) genes in B-cell tumors depends on the differentiation stage of the precursor normal cell.

Animals↗
PubMed1995

PCR mapping of integrons reveals several novel combinations of resistance genes.

The integron is a new type of mobile element which has evolved by a site-specific recombinational mechanism. Integrons consist of two conserved segments of DNA separated by a variable region containing one or more genes integrated as cassettes. Oligonucleotide probes specific for the conserved segments have revealed that integrons are widespread in recently isolated clinical bacteria. Also, by using oligonucleotide probes for several antibiotic resistance genes, we have found novel combinations of resistance genes in these strains. By using PCR, we have determined the content and order of the resistance genes inserted between the conserved segments in the integrons of these clinical isolates. PCR mapping of integrons can be a useful epidemiological tool to study the evolution of multiresistance plasmids and transposons and dissemination of antibiotic resistance genes.

Base Sequence↗
PubMed1992

Increased avidity of mutant IgM antibodies caused by the absence of COOH-terminal glycosylation of the mu H chain.

We have previously described the isolation of two hybridoma variants secreting higher avidity IgM (D5 and 7F5), starting from the E11 hybridoma cell line, which produces an antibody specific for the A Ag of the ABO blood group system. In order to explain at the molecular level this increased reactivity, cDNA encoding the H and L chains of the E11, D5, and 7F5 mAb were cloned and sequenced. Comparison of the nucleotide sequences showed a single point mutation in each of the two mAb produced by the hybridoma variants. The mutations were both located in the H chain C region and caused a Ser to Phe substitution at position 565 in the D5 mAb and a Asn to Tyr substitution at position 563 in the 7F5 mAb. Both substitutions modified the consensus glycosylation sequence (Asn-X-Ser/Thr) located in the tail piece of the secretory mu-chain. The absence of glycosylation at this site was confirmed by CNBr cleavage of the [14C]mannose-labeled mAb. The two single point mutations were solely responsible for the increased avidity of the antibodies, as confirmed by site-directed mutagenesis of the E11 mu-chain and serologic analysis of the mutated E11 antibodies. We conclude that the absence of glycosylation at Asn 563 is responsible for the increased avidity of the mutant, possibly by altering the quaternary structure of the IgM polymer. To our knowledge, this is the first report that point mutations in the H chain C region can influence the reactivity of IgM mAb.

Amino Acid Sequence↗