Insights into nuclear localization and dynamic association of CD38 in Raji and K562 cells.

CD38 is a type II transmembrane glycoprotein found mainly on the plasma membrane involved in the metabolism of cADPR and NAADP, two nucleotides with calcium mobilizing activity independent of inositol trisphosphate. Recent data report the presence of CD38 in different cellular compartments raising new questions about its effective role in cellular metabolism. In rat hepatocyte nuclei, CD38 has been proposed as a responsive to cADPR integral inner membrane protein suggesting that the nuclear envelope may also be an important source of Ca2+ stores. Further reports indicating that CD38 is localized in nuclear compartments in a variety of cell types and tissues including brain, liver, eye, spleen, and bone raise the condition of resolving the question concerning the effective presence of CD38 within the nucleus. Here we report data supporting the presence of CD38 at nuclear level independently of expression of surface CD38. We utilized two different human leukemia cell lines expressing or not expressing CD38 molecule on their cell surface. The morphological and biochemical results including enzymatic activity and proteomic determinations explain the effective nuclear localization of CD38 in human Raji and K562 cells. Since cell nucleus is a complex and highly dynamic environment with many functionally specialized regions, the nuclear localization of specific proteins represents an important mechanism in signal transduction. The presence of CD38 at the interchromatin region whether linked to nuclear scaffold or stored in nuclear structures as micronuclei and Cajal bodies co-localizing with coilin, suggests its involvement in nuclear processes including transcription, replication, repairing and splicing.