Retinoic acid-binding protein in experimental tumors and in tissues with metastatic tumor foci.

Screening for retinoic acid-binding protein (RABP) in experimental tumors revealed the presence of this protein in three mammary tumors, two metastatic colon tumors, B16 melanoma. Lewis lung carcinoma, Ridgway osteogenic sarcoma, and keratoacanthoma. RABP was below the limits of detection in two weakly metastatic colon tumors and in Sarcoma 180. After s.c. implantation of RABP-containing tumors into mice, this protein could be traced in the lungs due to pulmonary metastasis. Following implantation of Lewis lung tumors, RABP was detected in the lung on the 6th day. On the 15th day after implantation, RABP was present in lung and brain, but not in other tissues where this protein was normally lacking. In primary cultures of Lewis lung carcinoma, the lower limit for detection of RABP by sucrose gradient sedimentation technique corresponded to 0.12 mg protein that was extractable from 3 X 10(5) cells. Both chick embryo skin and rabbit ear skin extracts contained RABP; the level of cellular retinol-binding protein was high in chick embryo skin but only marginal in rabbit ear. The amounts of these proteins on chick embryo skin and rabbit ear skin correlate with the biological potency of retinol and retinoic acid, as observed by others.