Interleukin-2 transcriptional block by multifunctional Ca2+/calmodulin kinase

Area of Science:

• Immunology
• Molecular Biology
• Cell Signaling

Background:

• T-cell activation relies on calcium (Ca2+) influx, leading to interleukin-2 (IL-2) transcription via calcineurin in the presence of costimulation.
• In the absence of costimulation, Ca2+ influx induces T-cell anergy through an uncharacterized mechanism, involving an IL-2 transcriptional block.

Purpose of the Study:

• To investigate the molecular mechanisms underlying Ca2+-mediated T-cell anergy and identify key regulatory enzymes.
• To determine the role of Ca2+/calmodulin-dependent protein kinases (CaM kinases) in regulating IL-2 gene expression.

Main Methods:

• Utilized Jurkat T cells pretreated with a Ca2+ ionophore to induce anergy.
• Transfected cells with constitutively active mutants of various Ca2+/calmodulin-dependent enzymes, including multifunctional CaM kinase II, CaM kinase IV, calcineurin, and protein kinase C.
• Assessed the impact on inducible IL-2 reporter gene activity, beta-actin transcription, c-fos transcription, and Rous sarcoma virus promoter activity.

Main Results:

• Constitutively active multifunctional CaM kinase II transfection resulted in over 90% block of inducible IL-2 reporter gene activity.
• This inhibitory effect was specific to IL-2, with no significant changes observed in beta-actin or c-fos transcription.
• Multifunctional CaM kinase II also attenuated IL-2 activation mediated by calcineurin and phorbol ester, and T-cell receptor signaling activates this kinase.

Conclusions:

• Multifunctional CaM kinase, activated by T-cell receptor signaling, plays a critical role in mediating the anergy pathway by blocking IL-2 transcription.
• Both multifunctional CaM kinase and calcineurin are Ca2+/calmodulin-responsive enzymes that differentially regulate T-lymphocyte activation and anergy.
• These findings elucidate a novel mechanism for Ca2+ signal divergence in T-cell fate determination.