Douglas M. Gersten

Amino-terminal variation in melanoma antigens

Melanoma tumors express both common antigenic determinants and individually specific markers. A melanoma-specific glycoprotein antigen ( B700 ) with a molecular weight of approximately 65,000 daltons was detected on murine B16 melanoma cells but appears on other murine and human melanoma tumors. In order to determine the relationship between the B700 antigen and other melanoma antigens which have been described and to elucidate molecular changes that have taken place in the transformation from melanocyte to melanoma, we have purified the B700 glycoprotein to homogeneity. We have carried out amino acid composition analysis and partial sequence determinations and report that the B700 melanoma antigen shows similarities to serum albumin, but is not identical to this normal component. Moreover, amino-terminal variation occurs in the first 15 residues of the B700 antigen produced by separate B16 tumors.

B700, an albumin-like melanoma-specific antigen, is a vitamin D binding protein

B700, a murine melanoma-specific antigen, is a member of the serum albumin protein family. Other members include serum albumin and vitamin D binding protein. The primary structure and biochemical functions of B700, as well as its in vivo metabolic fate, are largely unknown. We compared murine albumin, vitamin D binding protein and B700 for their ability to specifically bind [3H]-1,25-dihydroxy-vitamin D3. Scatchard analysis revealed a single binding site for B700 with a Ka of 51,000 mol/l and a Bmax of 4.51 x 10(-7) mol/l. There was no significant difference in the Ka and Bmax among the albuminoid proteins. However, differences in the binding sites could be distinguished by competition experiments where vitamin D3, vitamin D2 or 7-dehydrocholesterol competed for the specific binding of 1.25-dihydroxyvitamin D3 to a greater extent by B700 than by vitamin D binding protein. The albumin binding site more closely resembles vitamin D binding protein than B700, but the data indicate that the binding function of the albuminoid proteins is conserved in B700.

Control of growth and vascularity of B16 melanoma by syngeneic lymphocytes

We have studied the participation of syngeneic lymphocytes in the subcutaneous growth and vascularization of B16 melanoma tumors. Subcutaneous tumors in animals, lymphocyte depleted by thymectomy and x-irradiation, exhibit slow, poorly vascularized growth as compared to normal or lymphocyte reconstituted controls. This condition may be reversed by administration of lymphocytes to lymphocyte deficient hosts either prior to tumor cell injection or while the animal is tumor bearing. The results are discussed in terms of lymphocyte induced angiogenesis.

Basis of tetracaine-induced inhibition of phagocytosis by cultured mouse peritoneal macrophages.

Abstract The inhibition of mouse peritoneal macrophage phagocytosis by the tertiary amine anesthetic, tetracaine, was studied in vitro . By investigating separately the recognition and ingestion phases of phagocytosis using 51 Cr-labeled sheep red blood cells (SRBC), the following observations were made. First, immune-mediated recognition of the SRBC via the opsonizing mouse immunoglobulin by the macrophages is inhibited by tetracaine. Second, non-immune recognition of unopsonized SRBC is not inhibited by tetracaine. Third, ingestion of the opsonized SRBC is inhibited by tetracaine to a greater extent than unopsonized SRBC. Fourth, the basis for the inhibition of recognition appears to be steric, probably related to anesthetic-induced clustering of receptors on the macrophage surface. Fifth, the results are discussed in terms of transmembrane control of macrophage receptors.

Comparison of the metabolic fate and tissue distribution of B700, an albumin-like melanoma-specific antigen with serum albumin in normal and tumor-bearing mice

1. B700, a murine melanoma antigen, is a member of the serum albumin protein family, being closely related to murine serum albumin (MSA). 2. We have studied and compared the metabolic fate and anatomic distribution of radioiodinated B700 and MSA administered to semisyngeneic naive and tumor-bearing mice. 3. Labelled material from both proteins is excreted primarily into urine. 4. The rate of excretion of the two proteins is markedly different, with B700 having a shorter half-life in the body. 5. Despite their similar molecular weights, intact B700 represents approx. 30% of the radioactivity in the urine but only 4% of the MSA in the urine is intact. 6. These studies demonstrate that the host can readily distinguish between very similar normal (MSA) and tumor-associated (B700) molecules and process them differently. 7. Similar findings of differential fate and distribution have been reported in comparing other albuminoid molecules [Dueland S., Blomhoff R. and Pedersen J. I. (1990) Biochem. J. 267, 721-725].

Protein Antigens of Mouse Melanomas

Two lines of evidence suggest that B16 melanoma cells express immunological determinants. The first is that syngeneic C57BL/6 mice may be immunized outright to B16 preparations—either whole-cell (Fidler et al., 1977) or extract (Bystryn, 1978). The second is that cultured cells, when injected into B16-sensitized hosts, exhibit in vivo behavior different from that observed following administration into naive hosts (Fidler et al.,1977; Gersten, 1980). It follows, then that B16 cells should possess unique molecules that are both absent from other C57BL/6 cells and immunogenic.