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 a 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.