The 3' UTR of the human CTLA4 mRNA can regulate mRNA stability and translational efficiency.

T cell activation results from the integration of signals generated through the T cell antigen receptor-CD3 complex with those from additional positive and negative regulatory pathways mainly mediated by the engagement of costimulatory receptors on T cells. Disruption of this balance leads to a defective immune response or alternative over-activation of the immune system. CTLA-4 plays a critical role in downregulating T cell responses. Autoimmune diseases have shown genetic linkage to the CTLA4 locus. In this report we demonstrate that the 3' UTR of CTLA4 regulates firefly luciferase reporter gene expression, can confer instability to CTLA4 mRNA and can influence its translation efficiency in vitro.

Phosphorylation of the activation loop tyrosines is required for sustained Syk signaling and growth factor-independent B-cell proliferation.

The Syk kinase is regarded as a promising target for the treatment of antigen-driven B-cell malignancies, considering its essential role in propagating antigenic stimuli through the B-cell receptor (BCR). In certain common B-cell malignancies Syk is activated even in the absence of BCR engagement, suggesting a wider role for this kinase in lymphomagenesis. In this paper, we have profiled molecular differences between BCR-induced and constitutive Syk activation in terms of phosphorylation of regulatory tyrosine residues, downstream signaling properties and capacity to sustain B-cell proliferation. Analysis of primary chronic lymphocytic leukemia B-cells and diffuse large B-cell lymphoma cell lines revealed that constitutive and BCR-induced Syk activation differ with respect to the phosphorylation status of the regulatory tyrosines at positions 352 and 525/526, with only the first site being phosphorylated in the case of constitutive and both sites in the case of BCR-induced Syk activation. Syk phosphorylated only on Y352 is capable of downstream signaling, as evidenced by experiments with a phosphomimetic mutant in which the activation loop tyrosines (YY525/526) were replaced with phenylalanines. However, phosphorylation at YY525/526 was shown to significantly increase the enzymatic activity of Syk and to be required for sustained PLCgamma2, Akt and ERK signaling as well as B-cell transformation. These data demonstrate that constitutively active Syk and Syk activated by BCR crosslinking represent separate stages of Syk activation with distinct signaling properties and transforming capacities.