Browsing by Author "Chen, Meng"

Background: Chronic pain is a highly prevalent and disabling concern among the 18 million cancer survivors in the United States, yet it is understudied. This study aimed to assess the time trends and related risk factors of chronic pain among cancer survivors. Methods: Using data from the National Health Interview Survey (NHIS), we included adult US cancer survivors from 2010 to 2021. Chronic pain was the outcome of interest, defined as pain on most days or every day during the past 3 months. Joinpoint regression models estimated annual percentage changes (APC) of chronic pain prevalence and multivariable logistic regression models estimated odds of experiencing chronic pain across different subgroups. Results: The final study sample included 377,509 respondents, with 39,473 (10.5%) reporting a history of cancer. Reported chronic pain prevalence decreased from 2016 among both cancer survivors (APC = -7.38%, 95% CI: -35.16%, 32.30%) and non-cancer individuals (APC = -4.71%, 95% CI: -12.34%, 3.59%). Compared to non-cancer individuals, cancer survivors had 20% higher odds of experiencing chronic pain (aOR = 1.20, 95% CI: 1.14, 1.27). Among cancer survivors, those with moderate depression had 40% higher odds of experiencing chronic pain (aOR = 1.40, 95% CI: 1.29, 1.52), while those with severe depression had 166% higher odds (aOR = 2.66, 95% CI: 2.34, 3.02), compared to those without depression. Conclusions: The association between chronic pain and depression calls for more targeted interventions or strategies towards pain management for cancer survivors to improve their life of quality and enhance overall survivorship.

When a plant emerges from the soil, it faces a critical developmental transition from utilizing stored energy to grow rapidly toward the light, to developing chloroplasts and beginning photosynthesis. While it is known that this process involves massive transcriptional reprogramming of the nuclear and plastidial genomes, the connections between chloroplast development and nuclear light signaling events are not well understood. One very promising target for investigating these connections is HEMERA (HMR), a dual-localized regulatory protein that is found in both nuclei and chloroplasts. HMR was previously identified as pTAC12, an essential component of the plastid-encoded RNA polymerase complex responsible for transcription of chloroplast photosynthetic genes. In the nucleus, HMR acts within the phytochrome signaling pathway as a transcriptional co-activator of a subset of growth-relevant genes in response to light, to regulate the elongation of the embryonic stem, or hypocotyl. HMR’s combination of roles in the nucleus and chloroplasts are dramatically demonstrated by the phenotypes of the hmr mutant, with a long hypocotyl and albino leaves when grown in the light.

While the functions of HMR in each compartment have been studied separately, the mechanisms by which the HMR protein is targeted to each compartment have not yet been determined. To address this, I characterized the localization signals of HMR with a combination of in vitro approaches and characterization of transgenic Arabidopsis lines. These experiments revealed that HMR has a cleavable N-terminal chloroplast transit peptide within its first 50 amino acids, while two predicted nuclear localization signals proved not to be highly functional. Surprisingly, HMR in the chloroplasts and nucleus appeared to both be the same cleaved form of the protein. We thus identified the mature form of HMR by mass spectrometry, finding that it begins from lysine as the result of transit peptide cleavage and possibly additional N-terminal processing. Through GST pull-down assays, we determined that this mature form of HMR was fully capable of interacting light signaling components. However, analysis of transgenic lines showed that expression of mature HMR alone could not complement the long-hypocotyl phenotype of the hmr mutant. Analysis of the transcription of HMR nuclear target genes confirmed that mature HMR lacked nuclear functionality.

Further investigation revealed that mature HMR does not accumulate within the nucleus, most likely as a result of its nonfunctional nuclear localization signals. However, addition of the transit peptide from the small subunit of Rubisco fully restored nuclear accumulation and function of mature HMR in Arabidopsis. Additional experiments testing the localization of a simple model of dual-targeted proteins with two types of localization signal showed that transit peptides might take priority over nuclear localization signals. These results together suggest an unexpected model of localization where HMR is first targeted to the chloroplasts, and then it is subsequently re-localized to the nucleus, thus connecting its nuclear and plastidial functions. Further investigation of this proposed retrograde plastid-to-nucleus translocation pathway promises to shed additional light on the link between nuclear light signaling events and chloroplast development.

Light is a critical environmental signal that regulates every phase of the plant life cycle, from germination to floral initiation. Of the many light receptors in the model plant Arabidopsis thaliana, the red- and far-red light-sensing phytochromes (phys) are arguably the best studied, but the earliest events in the phy signaling pathway remain poorly understood. One of the earliest phy signaling events is the translocation of photoactivated phys from the cytoplasm to the nucleus, where they localize to subnuclear foci termed photobodies; in continuous light, photobody localization correlates closely with the light-dependent inhibition of embryonic stem growth. Despite a growing body of evidence supporting the biological significance of photobodies in light signaling, photobodies have also been shown to be dispensable for seedling growth inhibition in continuous light, so their physiological importance remains controversial; additionally, the molecular components that are required for phy localization to photobodies are largely unknown. The overall goal of my dissertation research was to gain insight into the early steps of phy signaling by further defining the role of photobodies in this process and identifying additional intragenic and extragenic requirements for phy localization to photobodies.

Even though the domain structure of phys has been extensively studied, not all of the intramolecular requirements for phy localization to photobodies are known. Previous studies have shown that the entire C-terminus of phys is both necessary and sufficient for their localization to photobodies. However, the importance of the individual subdomains of the C-terminus is still unclear. For example a truncation lacking part of the most C-terminal domain, the histidine kinase-related domain (HKRD), can still localize to small photobodies in the light and behaves like a weak allele. However, a point mutation within the HKRD renders the entire molecule completely inactive. To resolve this discrepancy, I explored the hypothesis that this point mutation might impair the dimerization of the HKRD; dimerization has been shown to occur via the C-terminus of phy and is required for more efficient signaling. I show that this point mutation impairs nuclear localization of phy as well as its subnuclear localization to photobodies. Additionally, yeast-two-hybrid analysis shows that the wild-type HKRD can homodimerize but that the HKRD containing the point mutation fails to dimerize with both itself and with wild-type HKRD. These results demonstrate that dimerization of the HKRD is required for both nuclear and photobody localization of phy.

Studies of seedlings grown in diurnal conditions show that photoactivated phy can persist into darkness to repress seedling growth; a seedling's growth rate is therefore fastest at the end of the night. To test the idea that photobodies could be involved in regulating seedling growth in the dark, I compared the growth of two transgenic Arabidopsis lines, one in which phy can localize to photobodies (PBG), and one in which it cannot (NGB). Despite these differences in photobody morphology, both lines are capable of transducing light signals and inhibiting seedling growth in continuous light. After the transition from red light to darkness, the PBG line was able to repress seedling growth, as well as the accumulation of the growth-promoting, light-labile transcription factor PHYTOCHROME INTERACTING FACTOR 3 (PIF3), for eighteen hours, and this correlated perfectly with the presence of photobodies. Reducing the amount of active phy by either reducing the light intensity or adding a phy-inactivating far-red pulse prior to darkness led to faster accumulation of PIF3 and earlier seedling growth. In contrast, the NGB line accumulated PIF3 even in the light, and seedling growth was only repressed for six hours; this behavior was similar in NGB regardless of the light treatment. These results suggest that photobodies are required for the degradation of PIF3 and for the prolonged stabilization of active phy in darkness. They also support the hypothesis that photobody localization of phys could serve as an instructive cue during the light-to-dark transition, thereby fine-tuning light-dependent responses in darkness.

In addition to determining an intragenic requirement for photobody localization and further exploring the significance of photobodies in phy signaling, I wanted to identify extragenic regulators of photobody localization. A recent study identified one such factor, HEMERA (HMR); hmr mutants do not form large photobodies, and they are tall and albino in the light. To identify other components in the HMR-mediated branch of the phy signaling pathway, I performed a forward genetic screen for suppressors of a weak hmr allele. Surprisingly, the first three mutants isolated from the screen were alleles of the same novel gene, SON OF HEMERA (SOH). The soh mutations rescue all of the phenotypes associated with the weak hmr allele, and they do so in an allele-specific manner, suggesting a direct interaction between SOH and HMR. Null soh alleles, which were isolated in an independent, tall, albino screen, are defective in photobody localization, demonstrating that SOH is an extragenic regulator of phy localization to photobodies that works in the same genetic pathway as HMR.

In this work, I show that dimerization of the HKRD is required for both the nuclear and photobody localization of phy. I also demonstrate a tight correlation between photobody localization and PIF3 degradation, further establishing the significance of photobodies in phy signaling. Finally, I identify a novel gene, SON OF HEMERA, whose product is necessary for phy localization to photobodies in the light, thereby isolating a new extragenic determinant of photobody localization. These results are among the first to focus exclusively on one of the earliest cellular responses to light - photobody localization of phys - and they promise to open up new avenues into the study of a poorly understood facet of the phy signaling pathway.