There are 18 HDAC isoforms belonging to several classes, each with non-redundant functions and different cellular localizations, and all of these are expressed differentially in various tissues [127,128]; the following section will cover HDAC6, as it has a particular relevance to the UPS-autophagy axis, and development and treatment-resistance of GBM. The gene discussed is HDAC6; the disease is glioblastoma.