CREB1 and obesity due to melanocortin 4 receptor deficiency: Notably, in some cell types, phosphorylation might not be sufficient to promote CREB-dependent transcription, suggesting the existence of additional posttranslational modifications regulating CREB activity, including acetylation, sumoylation, glycosylation and ubiquitination.393 It is not known whether any of these putative CREB modifications occur at any stage of PDAC development in response to obesity, stress or a combination of obesity and stress.