Differential regulation of SOCS genes in normal and transformed erythroid cells

Abstract

The SOCS family of genes are negative regulators of cytokine signalling with SOCS-1 displaying tumor suppressor activity. SOCS-1, CIS and SOCS-3 have been implicated in the regulation of red blood cell production. In this study, a detailed examination was conducted on the expression patterns of these three SOCS family members in normal erythroid progenitors and a panel of erythroleukemic cell lines. Unexpectedly, differences in SOCS gene expression were observed during maturation of normal red cell progenitors, viz changes to CIS were inversely related to the alterations of SOCS-1 and SOCS-3. Similarly, these SOCS genes were differentially expressed in transformed erythoid cellserythroleukemic cells immortalized at an immature stage of differentiation expressed SOCS-1 and SOCS-3 mRNA constitutively, whereas in more mature cell lines SOCS-1 and CIS were induced only after exposure to erythropoietin (Epo). Significantly, when ectopic expression of the tyrosine kinase Lyn was used to promote differentiation of immature cell lines, constitutive expression of SOCS-1 and SOCS-3 was completely suppressed. Modulation of intracellular signalling via mutated Epo receptors in mature erythroleukemic lines also highlighted different responses by the three SOCS family members. Close scrutiny of SOCS-1 revealed that, despite large increases in mRNA levels, the activity of the promoter did not alter after erythropoietin stimulation; in addition, erythroid cells from SOCS-1À/À mice displayed increased sensitivity to Epo. These observations indicate complex, stagespecific regulation of SOCS genes during normal erythroid maturation and in erythroleukemic cells.

Csk-binding Protein Mediates Sequential Enzymatic Down-regulation and Degradation of Lyn in Erythropoietin-stimulated Cells

“…6B) when SOCS1 levels were at their highest (Ref. 17, data not shown). Unlike the association between Cbp and Ctk (Fig.…”

“…First, the phosphatase SHP-1 docks onto phosphorylated tyrosine residues of the receptor via its SH2 domain, and dephosphorylates the receptor (14). Second, several members of the suppressors of cytokine signaling (SOCS) family of negative regulators are activated upon Epo stimulation, including SOCS1, SOCS3, and cytokine-inducible SH2-domain-containing protein (CIS) (15)(16)(17). These proteins inhibit the kinase activity of JAK2 and compete with JAK2 and STAT5 for binding to activated receptors (18).…”

Lyn deficiency reduces GATA-1, EKLF and STAT5, and induces extramedullary stress erythropoiesis

“…Conversely, overexpression of Lyn in the immature R11 erythroid cell line enhanced GATA-1 and EKLF levels appreciably, and promoted spontaneous differentiation along the erythroid pathway (Sarna et al, 2003). Thus, alteration of Lyn activity within erythroid precursors influences key erythroid transcription factor levels, independent of Epo stimulation.…”

“…Bone marrow and splenic cell morphology were examined microscopically, following cytocentrifugation and Wright's Giemsa staining with, or without, neutral benzidine staining (McLeod et al, 1974). Flow cytometry was employed to assess cell surface expression of Ter119 (phycoerythrin-conjugated antimouse Ter119, BD Biosciences) and c-kit (fluorescein isothiocyanate-conjugated anti-mouse CD117, BD Biosciences), as detailed previously (Sarna et al, 2003) using an Epics XL/ MCL flow cytometer (Beckman-Coulter, Palo Alto, CA, USA). BFU-E and CFU-E were determined using methylcellulose cultures, as described elsewhere .…”

DYRK3 Dual-specificity Kinase Attenuates Erythropoiesis during Anemia

“…Negative feedback components integral to KIT and EPO receptor signaling circuits also are operative. These include SHP1 and PTP1B phosphatases (8,9), CIS, SOCS3, and SPRED1 as attenuators of JAK2 (Janus protein tyrosine kinase 2) and KIT kinases (5,10,11), and additional adaptor proteins within select signal transduction pathways (e.g. LNK and SH2B1) (12,13).…”