Described herein are isolated polypeptides having phosphatase and tensin homolog (PTEN) inhibitory activity, vectors and cells for the expression thereof and methods for their use in treating diseases associated with cytotoxic stress, such as spinal cord injury, stroke, traumatic brain injury, multiple sclerosis, Alzheimer's disease, amyotrophic lateral sclerosis (ALS), Parkinson's disease, and Huntington's disease.