Identification of an In Vivo MEK/WOX1 Complex as a Master Switch for Apoptosis in T Cell Leukemia

Area of Science:

• Cell Biology
• Immunology
• Molecular Biology

Background:

• Leukemia T cells exhibit variable susceptibility to apoptosis induced by phorbol myristate acetate (PMA).
• PMA at micromolar concentrations triggers apoptosis in Jurkat T cells via mitochondrial changes, granule release, and DNA fragmentation.
• The mitogen-activated protein kinase kinase 1 (MEK1) pathway, involving extracellular signal-regulated kinase (ERK), is implicated in PMA-induced apoptosis.

Purpose of the Study:

• To elucidate the molecular mechanism underlying differential susceptibility of leukemia T cells to PMA-induced apoptosis.
• To investigate the role of the proapoptotic tumor suppressor WOX1 (WWOX/FOR) and its interaction with MEK1 in T cell apoptosis.
• To determine if targeting the MEK1/WOX1 complex can modulate apoptosis in leukemia T cells.

Main Methods:

• Utilized Jurkat and Molt-4 T cell lines.
• Applied phorbol myristate acetate (PMA) to induce apoptosis.
• Employed chemical inhibitors U0126 and PD98059 to block MEK1/ERK signaling.
• Investigated protein-protein interactions using co-localization studies (lysosomes, lipid rafts, mitochondria).

Main Results:

• PMA induces apoptosis in Jurkat T cells through mitochondrial depolarization, cytosolic granule release, and DNA fragmentation.
• The MEK1 inhibitor U0126 prevents PMA-induced apoptosis by blocking MEK1 phosphorylation and subsequent relocation.
• Proapoptotic tumor suppressor WOX1 physically interacts with MEK1, and PMA disrupts this complex, leading to MEK1 relocation to lipid rafts and WOX1 to mitochondria.
• Molt-4 T cells, less differentiated, resist PMA-induced dissociation of the WOX1/MEK1 complex and are refractory to apoptosis.
• U0126 treatment overcomes this resistance in Molt-4 cells, enhancing apoptosis.

Conclusions:

• The in vivo MEK1/WOX1 complex acts as a critical regulator, functioning as an on/off switch for apoptosis in leukemia T cells.
• Differential regulation of the WOX1/MEK1 complex dissociation underlies the varying sensitivity of leukemia T cells to PMA-induced apoptosis.
• Targeting the MEK1/WOX1 interaction presents a potential therapeutic strategy for controlling leukemia T cell apoptosis.