HIF1A and mantle cell lymphoma: The decline of HIF-1α protein amount in MCL pretreated cells was faster than that without MCL treatment during the same period, suggesting that MCL accelerated the degradation of HIF-1α protein, as shown in Figure 4C. Since HIF-1α protein was degraded mainly through the ubiquitin-proteasome pathway, we performed immunoprecipitation experiments to detect the level of HIF-1α protein after a proteasome inhibitor (MG132) treatment in MCL-treated H1299 and Calu-1 cells.