B700, a melanoma‐specific antigen, catalyzes metabolism of prostaglandin E₂

Abstract

B700 is an albumin-like mouse-melanoma-specific antigen of unknown primary structure and biochemical function. The ability of mouse serum albumin to catalyze weak degradation of prostaglandin E2 has been utilized to compare functional similarities between B700 and mouse serum albumin. Both proteins catalyze the degradation of prostaglandin E2 to prostaglandin A2 and prostaglandin B2. This catalytic ability is related to the amino acid composition of the two proteins within the functional region rather than the 3-dimensional configuration, the activity is not altered upon boiling. The primary prostaglandin E2 metabolite in the presence of mouse serum albumin is prostaglandin B2, while prostaglandin A2 predominates in B700 catalyzed degradations. An additional product, presently unidentified, is produced during B700 catalyzed degradation of prostaglandin E2. Our studies indicate that the B700 protein has weak enzymatic activity for prostaglandin E2 similar to that of albumin. To our knowledge, B700 is the only melanoma antigen for which enzymatic activity has been demonstrated.

Proteinuria of B700, a 67 kD Albumin‐like Melanoma‐Specific Antigen

“…First, it is present on all murine melanomas, and cross-reactive molecules have been identified on all xenogeneic cultured melanomas studied, including those of humans, hamsters and mice (Gersten and Hearing, 1988). Second, B7OO is an "antenna" molecule, recognized by tumor-bearing hosts (Gersten et al, 1990). Third, antibodies to B700 are therapeutic (Gersten et al, 199213).…”

“…Two functional attributes of serum albumin which we have studied have been conserved in B700. Albumin's weak enzymatic activity, which interconverts prostaglandins (Farzaneh et al, 1990), and serum albumin's capacity to bind vitamin D compounds (Farzaneh et al, 1991a) are shared by B700.…”

Antigens of Murine Melanoma and Their Cross-Species Reactivity

“…C700) are albumin-like molecules [37][38][39][40][41], Hence, evolutionary gene duplication gave rise to C700 from serum albumin; B700 has then been produced by the tumor cells. While the consideration of these pro teins as members of the scrum albumin family of proteins is an interesting issue [42], here we are only concerned with B700 as a melanoma antigen.…”