The reasons why tumor cells metastasize to bone remain obscure. There is some evidence to support the theory that integrins (acting as cell surface adhesion receptors) play a role in mediating metastasis in certain organs. Here, we report that overexpression of a functionally active integrin alpha(v)b3 in Chinese hamster ovary (CHO) tumor cells drastically increased the incidence, number, and area of bone metastases in nude mice compared with those observed in mock-transfected CHO cells (CHO dhfr+) or in CHO cells expressing a functionally inactive integrin alpha(v)b3 (CHO beta3Delta744). Moreover, a breast cancer cell line (B02) established from bone metastases caused by MDA-MB-231 cells constitutively overexpressed integrin alpha(v)b3, whereas the cell surface expression level of other integrins remained unchanged. In vivo, the extent of bone metastases in B02-bearing mice was significantly increased compared with that of MDA-MB-231-bearing mice. In vitro, B02 cells and CHO cells expressing a functionally active integrin alpha(v)b3 exhibited substantially increased invasion of and adhesion to mineralized bone, bone sialoprotein, and collagen compared with those found with MDA-MB-231, CHO dhfr+, and CHO beta3Delta744 cells, respectively. Overall, our findings suggest that integrin alpha(v)b3 expression in tumor cells accelerates the development of osteolytic lesions, presumably through increased invasion of and adhesion to bone.

The integrin IIbβ3 mediates platelet aggregation through its fibrinogen and adhesive protein-binding properties. Particular interest concerns the role of the cytoplasmic domains of IIb and β3. We now report the molecular analysis of IIbβ3 from a patient with a Glanzmann’s thrombasthenia-like syndrome for whom the principal characteristics are an approximate 50% total platelet content of IIbβ3 but with a much lower proportion in the surface pool (Hardisty et al, Blood 80:696, 1992). Polymerase chain reaction (PCR) single-strand conformational polymorphism and DNA sequencing showed a heterozygous mutation giving rise to amino acid substitution R995 to Q in the GFFKR sequence of the cytoplasmic domain of IIb. Reverse transcriptase-PCR and polymorphism analysis only detected mRNA for the mutated allele of the IIb gene and a single allele of the β3 gene in his platelets, suggesting other unidentified defects. Site-directed mutagenesis followed by transient expression of the mutated IIb together with wild-type β3 in Cos-7 cells resulted in a markedly decreased expression of the complex at the cell surface when compared with cells transfected with wild-type IIb and β3. Flow cytometry with PAC-1 and a stable Chinese hamster ovary–transfected cell line showed that the mutated receptor was not locked into a high activation state, although it became so in the presence of the activating antibody, anti-LIBS6. This is the first reported natural mutation in the highly conserved GFFKR sequence of the IIb cytoplasmic domain.

Ultraviolet light at 254 nm induces various kinds of DNA damage. We have located and quantified the pyrimidine (6-4) pyrimidone photoproducts along three hundred and forty two nucleotides of SV40 DNA. The level of photoproduct induction varies greatly according to the position on the DNA, but unlike what happens with pyrimidine dimers, the very adjacent nucleotides do not play a major role in the frequency of formation. A new alkali-sensitive site has been found on the ACA sequence after UV irradiation. This complex lesion is insensitive to the T4 endonuclease V and the E. coli photolyase, and may be involved with mutagenesis.