Cholesterol homeostasis: ESCAPe from the ER

AbstractTranscriptional regulation and membrane traffic have traditionally been quite separate fields of biology, but they have been brought under the same roof by recent advances in understanding the cellular control of cholesterol metabolism

Membrane biogenesis and the unfolded protein response

In addition to serving as the entry point for newly translated polypeptides making their way through the secretory pathway, the endoplasmic reticulum (ER) also synthesizes many lipid components of the entire endomembrane system. A report published in this issue implicates a signaling pathway known to respond to ER unfolded protein load in the control of phospholipid biosynthesis by the organelle (Sriburi et al., 2004). The reasonable notion that demand for ER membrane is integrated with protein processing capacity was initially suggested by genetic analysis of yeast. The new data lend direct support for this idea and imply interesting mechanistic possibilities for how this coupling develops

Cod1p/Spf1p is a P-type ATPase involved in ER function and Ca2+ homeostasis

The internal environment of the ER is regulated to accommodate essential cellular processes, yet our understanding of this regulation remains incomplete. Cod1p/Spf1p belongs to the widely conserved, uncharacterized type V branch of P-type ATPases, a large family of ion pumps. Our previous work suggested Cod1p may function in the ER. Consistent with this hypothesis, we localized Cod1p to the ER membrane. The cod1Δ mutant disrupted cellular calcium homeostasis, causing increased transcription of calcium-regulated genes and a synergistic increase in cellular calcium when paired with disruption of the Golgi apparatus–localized Ca2+ pump Pmr1p. Deletion of COD1 also impaired ER function, causing constitutive activation of the unfolded protein response, hypersensitivity to the glycosylation inhibitor tunicamycin, and synthetic lethality with deletion of the unfolded protein response regulator HAC1. Expression of the Drosophila melanogaster homologue of Cod1p complemented the cod1Δ mutant. Finally, we demonstrated the ATPase activity of the purified protein. This study provides the first biochemical characterization of a type V P-type ATPase, implicates Cod1p in ER function and ion homeostasis, and indicates that these functions are conserved among Cod1p's metazoan homologues

Organ-specific lymphatic vasculature: From development to pathophysiology.

Recent discoveries of novel functions and diverse origins of lymphatic vessels have drastically changed our view of lymphatic vasculature. Traditionally regarded as passive conduits for fluid and immune cells, lymphatic vessels now emerge as active, tissue-specific players in major physiological and pathophysiological processes. Lymphatic vessels show remarkable plasticity and heterogeneity, reflecting their functional specialization to control the tissue microenvironment. Moreover, alternative developmental origins of lymphatic endothelial cells in some organs may contribute to the diversity of their functions in adult tissues. This review aims to summarize the most recent findings of organotypic differentiation of lymphatic endothelial cells in terms of their distinct (patho)physiological functions in skin, lymph nodes, small intestine, brain, and eye. We discuss recent advances in our understanding of the heterogeneity of lymphatic vessels with respect to the organ-specific functional and molecular specialization of lymphatic endothelium, such as the hybrid blood-lymphatic identity of Schlemm's canal, functions of intestinal lymphatics in dietary fat uptake, and discovery of meningeal lymphatic vasculature and perivascular brain lymphatic endothelial cells