AKT1 and cancer: Finally, while the 35-kDa LAPTM4b isoform has been shown to promote cancer via binding to p85 of PI3K and PI3K/Akt activation16, 17, it is possible that the 24-kDa isoform, which lacks the binding site for p85, also has a role in cancer promotion by enhancing mTORC1 activation via amino acids, a finding supported by our observed stimulation of cell growth and proliferation by this LAPTM4b isoform.