Human MM cell growth by p62^−/− stromal cells. (A) Marrow stromal cells from p62^−/− or p62^+/− mice were cocultured with GFP-labeled MM1.S cells for 3 days. Identification of MM cells was performed by fluorescence microscopy. Results represent the mean (± SEM) for 4 determinations. *P < .01 compared with cultures containing stromal cells from p62^+/− mice. (B) IL-6 and TNF-α production in cocultures of human MM cells with p62^−/− or p62^+/− mouse marrow stromal cells. Stromal cells from p62^−/− or p62^+/− littermates were cocultured with MM1.S cells for 3 days. The conditioned media were harvested and assayed using commercially available ELISAs. Results represent the mean (± SEM) for 4 determinations. *P < .01 compared with cultures containing p62^+/− stromal cells. (C) VCAM-1 expression on stromal cells. Stromal cells from the p62^−/− or p62^+/− littermates were cultured for 3 days, the cell lysates were collected, and analyzed by Western blot using anti–mouse VCAM-1. (D) VCAM-1 mRNA levels in p62^+/− or p62^−/− bone marrow stromal cells cocultured with MM1.S. Marrow stromal cells from p62^+/− or p62^−/− mice were cocultured with MM1.S cells for 3 days, the myeloma cells removed by vigorous washing as described in “Discussion,” and murine VCAM-1 mRNA was quantitated by quantitative PCR. Similar results were seen in 3 independent experiments.