To understand how light might entrain a mammalian circadian clock, we examined the effects of light on mPer1, a sequence homolog of Drosophila per, that exhibits robust rhythmic expression in the SCN. mPer1 is rapidly induced by short duration exposure to light at levels sufficient to reset the clock, and dose-response curves reveal that mPer1 induction shows both reciprocity and a strong correlation with phase shifting of the overt rhythm. Thus, in both the phasing of dark expression and the response to light mPer1 is most similar to the Neurospora clock gene frq. Within the SCN there appears to be localization of the induction phenomenon, consistent with the localization of both light-sensitive and light-insensitive oscillators in this circadian center.

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Transcript levels of DBP, a member of the PAR leucine zipper transcription factor family, exhibit a robust rhythm in suprachiasmatic nuclei, the mammalian circadian center. Here we report that DBP is able to activate the promoter of a putative clock oscillating gene, mPer1, by directly binding to the mPer1 promoter. The mPer1 promoter is cooperatively activated by DBP and CLOCK-BMAL1. On the other hand, dbp transcription is activated by CLOCK-BMAL1 through E-boxes and inhibited by the mPER and mCRY proteins, as is the case for mPer1. Thus, a clock-controlled dbp gene may play an important role in central clock oscillation.Most eukaryotes and some prokaryotes have circadian (ϳ24-h) rhythms governed by endogenous oscillators that control daily rhythms in physiology and behavior. Recent molecular dissections in cyanobacteria, Neurospora, Drosophila, and mice have revealed that oscillations in the transcription of specific clock genes play a central role in the generation of circadian rhythms and that negative feedback loops, in which certain gene products suppress their own transcription, form central elements of the mechanism of the circadian oscillator conserved across species (5, 17).In mammals, the suprachiasmatic nucleus (SCN) is known as the anatomical locus of a dominant mammalian pacemaker for circadian behavior and hormonal rhythms (16,21). Following the initial discovery of mPer1 in the SCN (31) (Sun et al. reported the same gene, RIGUI, independently [28]), the first mammalian homologue of the Drosophila clock gene per (4, 13), many noticed that this gene is one of three genes of the mammalian period gene family; Per2 (1,26,29) and Per3 (30, 36) are also abundantly expressed in neurons of the SCN.Among mammalian per homologues, evidence has accumulated that at least mPer1 is a component constituting the central oscillatory mechanism. First, transcripts of mPer1 show a very robust rhythm in the SCN in mice (28, 31) and rats (35), even in extended constant dark (DD) conditions (27). Second, the auto-negative feedback loop seems to be closed for the mPer1 gene, as with the Drosophila per gene product PER, which negatively regulates the expression of its own gene (per) (11). The transcription of mPer1 was shown to be activated by the binding of the CLOCK-BMAL1 complex to the E-boxes (CACGTG) in the promoter region of the mPer1 gene (9), and this activation is specifically inhibited by PER1 protein and other negative elements, including PER2, PER3, TIM, CRY1, and CRY2 (14,18,23,24). Third and perhaps more important is the finding that mPer1 expression parallels the behavioral rhythm (27). mPer1 is rapidly induced by light in a time-of-day and tissue-specific manner that correlates well with the resetting behavior of the overt rhythm in locomotor activity. Moreover, the photic thresholds and dose responses for the two processes are quantitatively very similar, and each shows reciprocity between light intensity and duration (27).Besides the clock genes constituting this core oscillatory loop, a transcription fa...

The mechanism whereby brief light exposure resets the mammalian circadian clock in a phase dependent manner is not known, but is thought to involve Per gene expression. At the behavioural level, a light pulse produces phase delays in early subjective night, phase advances in late subjective night, and no phase shifts in mid-subjective night or subjective day. To understand the relationship between Per gene activity and behavioural phase shifts, we examined light-induced mPer1 and mPer2 expression in the suprachiasmatic nucleus (SCN) of the mouse, in the subjective night, with a view to understanding SCN heterogeneity. In the VIP-containing region of the SCN (termed `core'), light-induced mPer1 expression occurs at all times of the subjective night, while mPer2 induction is seen only in early subjective night. In the remaining regions of the SCN (termed `shell'), a phase delaying light pulse produces no mPer1 but significant mPer2 expression, while a phase advancing light pulse produces no mPer2 but substantial mPer1 induction. Moreover, following a light pulse during mid-subjective night, neither mPer1 nor mPer2 are induced in the shell. The results reveal that behavioural phase shifts occur only when light-induced Per gene expression spreads from the core to the shell SCN, with mPer1 expression in shell corresponding to phase advances, and mPer2 corresponding to phase delays. The results indicate that the time course and the localization of light-induced Per gene expression in SCN reveals important aspects of intra-SCN communication.

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Ferroptosis, a novel form of programmed cell death, is characterized by iron-dependent lipid peroxidation and has been shown to be involved in multiple diseases, including cancer. Stimulating ferroptosis in cancer cells may be a potential strategy for cancer therapy. Therefore, ferroptosis-inducing drugs are attracting more attention for cancer treatment. Here, we showed that erianin, a natural product isolated from Dendrobium chrysotoxum Lindl, exerted its anticancer activity by inducing cell death and inhibiting cell migration in lung cancer cells. Subsequently, we demonstrated for the first time that erianin induced ferroptotic cell death in lung cancer cells, which was accompanied by ROS accumulation, lipid peroxidation, and GSH depletion. The ferroptosis inhibitors Fer-1 and Lip-1 but not Z-VAD-FMK, CQ, or necrostatin-1 rescued erianin-induced cell death, indicating that ferroptosis contributed to erianin-induced cell death. Furthermore, we demonstrated that Ca2+/CaM signaling was a critical mediator of erianin-induced ferroptosis and that blockade of this signaling significantly rescued cell death induced by erianin treatment by suppressing ferroptosis. Taken together, our data suggest that the natural product erianin exerts its anticancer effects by inducing Ca2+/CaM-dependent ferroptosis and inhibiting cell migration, and erianin will hopefully serve as a prospective compound for lung cancer treatment.

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The mPer1 gene is assumed to be a key molecule in the regulation and functioning of the mammalian circadian clock, which is based on the oscillation generated by a transcription-(post)translation feedback loop of a set of clock genes [1]. Robust circadian oscillation and acute light-elicited induction of mPer1 mRNA expression have been observed in the suprachiasmatic nucleus (SCN), the mammalian circadian center [2] [3]. To investigate the mechanism underlying the complex regulation of mPer1 expression, we isolated and characterized the 5' upstream region of the mPer1 gene. Unexpectedly, we identified two promoters, each followed by alternative first exons of mPer1. Consistent with the presence of multiple E-boxes in the promoters, exon-specific in situ hybridization of the SCN established that both promoters function in circadian oscillation and in light-induction of mPer1 expression. Transgenic mice carrying the 5' upstream region of the mPer1 gene fused to the luciferase gene demonstrated that a DNA fragment carrying both promoter regions is sufficient to elicit striking circadian oscillation in the SCN and responsiveness to light. Moreover, luminescence in the SCN accurately mirrored the mPer1 transcriptional activity. These transgenic mice will be very useful for monitoring clock-specific mPer1 expression in intact organisms and to follow the circadian clock in real time.