Examination of Parameters Influencing [3H]MK-801 Binding in Postmortem Human Cortex

[3H]MK-801 binding was used as an index of the glutamate receptor N-methyl-D-aspartate-subtype channel to examine the influence of gender, age, mode of death (agonal status), interval between death and autopsy (postmortem delay), and time in storage at -70 degrees C in well washed homogenate preparations from postmortem human frontal cortex. Basal binding and the modulatory effects of glutamate, glycine, spermidine, and zinc were examined with respect to these variables. Basal binding was sensitive to agonal status, being higher in sudden death cases. The effect of added glutamate and glycine was sensitive to age, with a trend toward lower binding with increasing age. The effect of added spermidine alone was sensitive to storage time at -70 degrees C, the binding being higher with longer storage time. The effect of added zinc was also sensitive to postmortem delay, with zinc causing a greater reduction in binding with shorter postmortem delays. Thus, with the exception of gender, all variables examined influenced [3H]MK-801 binding, highlighting the attention that should be given to these factors in postmortem studies in normal and diseased human subjects.     

miR-125b promotes cell death by targeting spindle assembly checkpoint gene MAD1 and modulating mitotic progression

The spindle assembly checkpoint (SAC) is a ‘wait-anaphase'' mechanism that has evolved in eukaryotic cells in response to the stochastic nature of chromosome–spindle attachments. In the recent past, different aspects of the SAC regulation have been described. However, the role of microRNAs in the SAC is vaguely understood. We report here that Mad1, a core SAC protein, is repressed by human miR-125b. Mad1 serves as an adaptor protein for Mad2 – which functions to inhibit anaphase entry till the chromosomal defects in metaphase are corrected. We show that exogenous expression of miR-125b, through downregulation of Mad1, delays cells at metaphase. As a result of this delay, cells proceed towards apoptotic death, which follows from elevated chromosomal abnormalities upon ectopic expression of miR-125b. Moreover, expressions of Mad1 and miR-125b are inversely correlated in a variety of cancer cell lines, as well as in primary head and neck tumour tissues. We conclude that increased expression of miR-125b inhibits cell proliferation by suppressing Mad1 and activating the SAC transiently. We hypothesize an optimum Mad1 level and thus, a properly scheduled SAC is maintained partly by miR-125b.