MAPK13 and cancer: Moreover, p38α and p38β are ubiquitously expressed, p38α usually at higher levels than p38β except in some brain regions, whereas p38γ and p38δ expression tends to be more tissue-specific, p38γ (MAPK12/ERK6) in muscle, and p38δ (MAPK13/SAPK4) in lung and kidney [11].p38 demonstrates distinct and even opposing effects in different cancers, as it was shown to serve either as a tumor suppressor or tumor promoter.