Tubuloreticular structures in S49 cells. Relation to cAMP-dependent protein kinase

Tubuloreticular structures (TRS) occur spontaneously in S49 mouse lymphoma cells grown in suspension culture. These structures appear in approx. 20% of the cells in electron microscopical cross-sections. Cloning of S49 cells in semi-solid agarose reveals that TRS are potentially present in all S49 cells. An increase of 60% in the frequency of TRS was observed following exposure of S49 cells to 2 X 10(-4) db-cAMP. This increase was not observed in mutant S49 cells lacking cAMP-dependent protein kinase activity. The data suggest that one possibility for the regulation of TRS is through a pathway involving cAMP-dependent protein kinase. In addition, TRS also appear in tumors derived from S49 cells and therefore serve as an ultrastructural cytoplasmic marker for these cells, both in culture and in syngeneic hosts. We suggest the S49 cells as a model system for studying the regulation and function of tubuloreticular structures in vitro and in vivo in malignant lymphoid cells.