Protein kinase Cdelta (PKCdelta) is an important regulator of apoptosis in epidermal keratinocytes. However, little information is available regarding the downstream kinases that mediate PKCdelta-dependent keratinocyte death. This study implicates p38delta mitogen-activated protein kinase (MAPK) as a downstream carrier of the PKCdelta-dependent death signal. We show that coexpression of PKCdelta with p38delta produces profound apoptosis-like morphological changes. These morphological changes are associated with increased sub-G(1) cell population, cytochrome c release, loss of mitochondrial membrane potential, caspase activation, and PARP cleavage. This death response is specific for the combination of PKCdelta and p38delta and is not produced by replacing PKCdelta with PKCalpha or p38delta with p38alpha. A constitutively active form of MEK6, an upstream activator of p38delta, can also produce cell death when coupled with p38delta. In addition, concurrent p38delta activation and extracellular signal-regulated kinase 1/2 (ERK1/2) inactivation are required for apoptosis. Regarding this inverse regulation, we describe a p38delta-ERK1/2 complex that may coordinate these changes in activity. We further show that this p38delta-ERK1/2 complex relocates into the nucleus in response to PKCdelta expression. This regulation appears to be physiological, since H(2)O(2), a known inducer of keratinocyte apoptosis, promotes identical PKCdelta and p38delta-ERK1/2 activity changes, leading to similar morphological changes.