Cytosolic PRKD1, 2 and 3 (protein kinase D1, D2 and D3) catalyze the phosphorylation of serine residue 132 of isoform 2 of ceramide transfer protein (COL4A3BP-2, CERT). Protein kinase D (PRKD) is as a crucial regulator of secretory transport at the trans-Golgi network (TGN). Phosphorylation of COL4A3BP-2 reduces its ceramide transfer activity. PRKDs may therefore act as regulators of lipid homeostasis (Fugmann et al. 2007).