Modulation of disease severity of dystrophic epidermolysis bullosa by a splice site mutation in combination with a missense mutation in the COL7A1 gene.

Dystrophic epidermolysis bullosa (EBD) is a clinically heterogeneous skin disorder, characterized by abnormal anchoring fibrils (AF) and loss of dermal-epidermal adherence. EBD has been linked to the COL7A1 gene at chromosome 3p21 which encodes collagen VII, the major component of the AF. Here we investigated two unrelated EBD families with different clinical phenotypes and novel combinations of recessive and dominant COL7A1 mutations. Both families shared the same recessive heterozygous 14 bp deletion at the exon-intron 115 boundary of the COL7A1 gene. The deletion caused in-frame skipping of exon 115 and the elimination of 29 amino acid residues from the pro-alpha1(VII) polypeptide chain. As a result, procollagen VII was not converted to collagen VII and the C-terminal NC-2 propeptide which is normally removed from the procollagen VII prior to formation of the anchoring fibrils was retained in the skin. All affected individuals also carried missense mutations in exon 73 of COL7A1 which lead to different glycine-to-arginine substitutions in the triple-helical domain of collagen VII. Combination of the deletion mutation with a G2009R substitution resulted in a mild phenotype. In contrast, combination of the deletion with a G2043R substitution led to a severe phenotype. The G2043R substitution was a de novo mutation which alone caused a mild phenotype. Thus, different combinations of dominant and recessive COL7A1 mutations can modulate disease activity of EBD and alter the clinical presentation of the patients.

An 80 Kb P1 clone from chromosome 3p21.3 suppresses tumor growth in vivo.

High frequencies of allelic loss on the short arm of chromosome 3 in small cell lung cancer (SCLC) and a number of other tumors suggest the existence of a tumor suppressor gene(s) within the deleted regions. Two small cell lung cancer lines, NCI H740 and GLC20, have been described which have homozygous deletions in the region 3p21.3. The deleted region overlaps with a 2 Mb fragment of human DNA present in the interspecies hybrid HA(3)BB9F, that suppresses tumor formation by mouse A9 fibrosarcoma cells. Human sequences from this cell hybrid were isolated using inter Alu PCR. From this starting point, a P1 contig was developed for the region of 450 Kb that is common to the homozygous deletions seen in the SCLC lines NCI H740 and GLC20 and is also present in HA(3)BB9F, the suppressed A9 hybrid. Individual P1 clones were assayed for their ability to suppress the tumorigenicity of the mouse fibrosarcoma cell line A9 as assayed by injection of transfected A9 cells into athymic nude mice. The introduction of one of the P1 clones into A9 cells resulted in suppression of tumor growth whereas two other P1 clones from the contig failed to suppress tumor formation in athymic nude mice. These data functionally delimit a tumor suppressor locus to a region of 80 kb within a P1 clone at 3p21.3.

Isolation of the human semaphorin III/F gene (SEMA3F) at chromosome 3p21, a region deleted in lung cancer.

Small cell lung cancer (SCLC) has been correlated with a deletion in the short arm of chromosome 3, with the region 3p21 being lost from one homolog in almost all cases. Two SCLC cell lines have homozygous deletions in 3p21, and these deletions overlap with a fragment of chromosome 3 that has tumor suppression activity in vivo. We have isolated some cDNA clones from this region that are homologous to the genes constituting the semaphorin family. They represent a novel human semaphorin, termed sema III/F (HGMW-approved symbol SEMA3F), which is expressed as a 3.8-kb transcript in a variety of cell lines and tissues; it is detected as early as Embryonic Day 10 in mouse development. There is high expression in mammary gland, kidney, fetal brain, and lung and lower expression in heart and liver. Although there is reduced expression of this gene in several SCLC lines, no mutations were found. This semaphorin homolog has characteristics of a secreted member of the semaphorin III family, with 52% identity with mouse semaphorin E and 49% identity with chicken collapsin/semaphorin D.

Subpopulations of CD8+ cytotoxic T cell precursors collaborate in the absence of conventional CD4+ helper T cells.

Four different subpopulations (Ly6Cneg, Ly6Clow, Ly6Cint, and Ly6Chi) of CD8+ T cells were arbitrarily defined on the basis of differential expression of Ly6C Ag. By combining the processes of electronic cell sorting and automated cell deposition, small numbers of respective CD8+ T cell subpopulations were directly deposited into tissue culture wells in which mitogen-stimulated responses were studied. Anti-CD3-stimulated proliferation and IL-2 production were the strongest by Ly6Cneg/Ly6Clow T cells, moderate for Ly6Cint T cells, and highly deficient for Ly6Chi T cells. The level of IL-2 production for Ly6Cneg CD8+ T cells was comparable to that of conventional CD4+ Th cells. Allogeneic stimulator cells elicited a strong cytotoxic response by Ly6Cneg + low but not Ly6Chi CD8+ T cells in the absence of added lymphokines. When IL-2 was supplied in excess, anti-CD3 induced comparable levels of cell proliferation and cytotoxic activity in Ly6Cneg, Ly6Clow, Ly6Cint, and Ly6Chi CD8+ T cells whereas alloantigen stimulated an approximate fivefold higher cytotoxic response by Ly6Chi than Ly6Cneg + low CD8+ T cells. Stimulation of co-cultures of B10 (CD8b) Ly6Cneg + low and congenic B10.CD8a Ly6Chi CD8+ T cells in the absence of added lymphokines, followed by selective elimination of activated CD8.1+ (CD8.2+) T cells by anti-CD8.1 (anti-CD8.2) + C treatment, allowed the demonstration that help provided by Ly6Cneg + low T cells can be effectively used by both Ly6Cneg + low and Ly6Chi T cells in anti-CD3 and alloantigen induced proliferative and cytotoxic responses, respectively.