The response of HR-MM cells to hypoxia. (A) The growth of parental cells (RPMI8226, KMS-11, U266) and HR-MM cells (RPMI8226-HR, KMS-11-HR, U266-HR) were measured after 24, 48, and 72 hours of normoxic (20% O2) or hypoxic (1% O2) culture conditions. (B) The expression level of HIF-1α protein in parental cells and HR-MM cells cultured under 20% or 1% O2 conditions for 24 hours. Numbers below the panels represent the normalized HIF-1α expression signal by β-actin (ratio).