The retinoid induced pancreatic cancer redifferentiation-apoptosis sequence and the mitochondria: a suggested obligatory sequence of events.

Retinoic acid induces redifferentiation and apoptosis in pancreatic adenocarcinoma cell lines. Redifferentiation includes early reversion into aerobic metabolism as reflected by an increase of mitochondrial activity and mass with normal membrane potential and terminal ductal cell differentiation. Cells in such a state either attempt to correct their DNA abnormalities or commit suicide by apoptosis. In some cell systems, such as pancreatic ductal cells, the stem cells show potential to transdifferentiate into functional normal endocrine cell type. However, since it is impossible to correct a highly corrupted genome, cells eventually succumb to apoptosis. Mitochondrial changes appear to be the enforcing factor for this process. The Transformation--Normalizing-redifferentiation--Apoptosis sequence has been shown by several studies, utilizing various cell types, apoptotic inducers, biomarkers and time frames. Although some studies have shown concomitant apoptosis and redifferentiation, others have reported apoptosis without prior redifferentiation. However, utilizing the appropriate time frame and the markers of earlier mitochondrial changes, one would detect a scenario similar to the retinoid model. This situation can be achieved by delaying apoptosis or reducing the inducer concentration in such systems. The final physiological fate of a normal terminally differentiated cells is apoptosis. Similarly, it is suggested that a degree of normalizing redifferentiation of transformed cells might be expected prior to apoptosis. The former seemed obligatory at least in the retinoid-pancreatic model.