Class I phosphoinositide 3-kinase (PI3K) generates phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)
) at the plasma membrane in response to growth factors, activating a signalling cascade that ...regulates many cellular functions including cell growth, proliferation, survival, migration and metabolism. The PI3K pathway is commonly dysregulated in human cancer, and drives tumorigenesis by promoting aberrant cell growth and transformation. PtdIns(3,4,5)
facilitates the activation of many pleckstrin homology (PH) domain-containing proteins including the serine/threonine kinase AKT. There are three AKT isoforms that are frequently hyperactivated in cancer through mutation, amplification or dysregulation of upstream regulatory proteins. AKT isoforms have converging and opposing functions in tumorigenesis. PtdIns(3,4,5)
signalling is degraded and terminated by phosphoinositide phosphatases such as phosphatase and tensin homologue (PTEN), proline-rich inositol polyphosphate 5-phosphatase (PIPP) (INPP5J) and inositol polyphosphate 4-phosphatase type II (INPP4B). PtdIns(3,4,5)
is rapidly hydrolysed by PIPP to generate phosphatidylinositol 3,4-bisphosphate (PtdIns(3,4)
), which is further hydrolysed by INPP4B to form phosphatidylinositol 3-phosphate (PtdIns3
). PtdIns(3,4)
and PtdIns3
are also important signalling molecules; PtdIns(3,4)
together with PtdIns(3,4,5)
are required for maximal AKT activation and PtdIns3
activates PI3K-dependent serum and glucocorticoid-regulated kinase (SGK3) signalling. Loss of
or
expression or function promotes tumour growth in murine cancer models through enhanced AKT isoform-specific signalling. INPP4B inhibits PtdIns(3,4)
-mediated AKT activation in breast and prostate cancer; however, INPP4B expression is increased in acute myeloid leukaemia (AML), melanoma and colon cancer where it paradoxically promotes cell proliferation, transformation and/or drug resistance. This review will discuss how PTEN, PIPP and INPP4B distinctly regulate PtdIns(3,4,5)
signalling downstream of PI3K and how dysregulation of these phosphatases affects cancer outcomes.
Inositol polyphosphate 4-phosphatase-II (INPP4B) is a regulator of the phosphoinositide 3-kinase (PI3K) signaling pathway and is implicated as a tumor suppressor in epithelial carcinomas. INPP4B loss ...of heterozygosity (LOH) is detected in some human breast cancers; however, the expression of INPP4B protein in breast cancer subtypes and the normal breast is unknown. We report here that INPP4B is expressed in nonproliferative estrogen receptor (ER)-positive cells in the normal breast, and in ER-positive, but not negative, breast cancer cell lines. INPP4B knockdown in ER-positive breast cancer cells increased Akt activation, cell proliferation, and xenograft tumor growth. Conversely, reconstitution of INPP4B expression in ER-negative, INPP4B-null human breast cancer cells reduced Akt activation and anchorage-independent growth. INPP4B protein expression was frequently lost in primary human breast carcinomas, associated with high clinical grade and tumor size and loss of hormone receptors and was lost most commonly in aggressive basal-like breast carcinomas. INPP4B protein loss was also frequently observed in phosphatase and tensin homolog (PTEN)-null tumors. These studies provide evidence that INPP4B functions as a tumor suppressor by negatively regulating normal and malignant mammary epithelial cell proliferation through regulation of the PI3K/Akt signaling pathway, and that loss of INPP4B protein is a marker of aggressive basal-like breast carcinomas.
Abstract
In preparation for the 2021 Centers for Disease Control and Prevention (CDC) sexually transmitted infections (STIs) treatment guidelines, the CDC convened an advisory group in 2019 to ...examine recent literature addressing updates in the epidemiology, diagnosis, and management of STIs. This article summarizes recent data in each of these key topic areas as they pertain to bacterial vaginosis (BV), the most common cause of vaginal discharge. The evidence reviewed primarily focused on updates in the global epidemiology of BV, risk factors for BV, data supportive of sexual transmission of BV-associated bacteria, BV molecular diagnostic tests, and novel treatment regimens. Additionally, recent literature on alcohol abstinence in the setting of 5-nitroimidazole use was reviewed.
Genetic factors predictive of severe adolescent idiopathic scoliosis (AIS) are largely unknown. To identify genetic variation associated with severe AIS, we performed an exome-wide association study ...of 457 severe AIS cases and 987 controls. We find a missense SNP in SLC39A8 (p.Ala391Thr, rs13107325) associated with severe AIS (P = 1.60 × 10
, OR = 2.01, CI = 1.54-2.62). This pleiotropic SNP was previously associated with BMI, blood pressure, cholesterol, and blood manganese level. We replicate the association in a second cohort (841 cases and 1095 controls) resulting in a combined P = 7.02 × 10
, OR = 1.94, CI = 1.63-2.34. Clinically, the minor allele of rs13107325 is associated with greater spinal curvature, decreased height, increased BMI and lower plasma manganese in our AIS cohort. Functional studies demonstrate reduced manganese influx mediated by the SLC39A8 p.Ala391Thr variant and vertebral abnormalities, impaired growth, and decreased motor activity in slc39a8 mutant zebrafish. Our results suggest the possibility that scoliosis may be amenable to dietary intervention.
Autophagic lysosome reformation (ALR) recycles autolysosome membranes formed during autophagy, to make lysosomes and is essential for continued autophagy function. Localized membrane remodeling on ...autolysosomes leads to the extension of reformation tubules, which undergo scission to form new lysosomes. The phosphoinositides phosphatidylinositol-4-phosphate (PtdIns4P) and phosphatidylinositol-4,5-bisphosphate (PtdIns4,5P
) induce this remodeling by recruiting protein effectors to membranes. We identified the inositol polyphosphate 5-phosphatase INPP5K, which converts PtdIns(4,5)P
to PtdIns4P is essential for ALR in skeletal muscle.
mutations that reduce its 5-phosphatase activity are known to cause muscular dystrophy, via an undefined mechanism. We generated skeletal muscle-specific
knockout mice which exhibited severe muscle disease, with lysosome depletion and marked autophagy inhibition. This was due to decreased PtdIns4P and increased PtdIns(4,5)P
on autolysosomes, causing reduced scission of reformation tubules. ALR was restored in cells with loss of INPP5K by expression of wild-type INPP5K, but not muscle-disease causing mutants. Therefore on autolysosomes, both PtdIns(4,5)P
generation and its removal by INPP5K is required for completion of ALR. Furthermore, skeletal muscle shows a dependence on the membrane recycling ALR pathway to maintain lysosome homeostasis and ensure the protective role of autophagy against disease.
Chronic reactive oxygen species (ROS) production by mitochondria may contribute to the development of insulin resistance, a primary feature of type 2 diabetes. In recent years it has become apparent ...that ROS generation in response to physiological stimuli such as insulin may also facilitate signaling by reversibly oxidizing and inhibiting protein tyrosine phosphatases (PTPs). Here we report that mice lacking one of the key enzymes involved in the elimination of physiological ROS, glutathione peroxidase 1 (Gpx1), were protected from high-fat-diet-induced insulin resistance. The increased insulin sensitivity in
Gpx1
−/− mice was attributed to insulin-induced phosphatidylinositol-3-kinase/Akt signaling and glucose uptake in muscle and could be reversed by the antioxidant N-acetylcysteine. Increased insulin signaling correlated with enhanced oxidation of the PTP family member PTEN, which terminates signals generated by phosphatidylinositol-3-kinase. These studies provide causal evidence for the enhancement of insulin signaling by ROS in vivo.
Macroautophagy/autophagy occurs basally under nutrient-rich conditions in most mammalian cells, contributing to protein and organelle quality control, and protection against aging and ...neurodegeneration. During autophagy, lysosomes are heavily utilized via their fusion with autophagosomes and must be repopulated to maintain autophagic degradative capacity. During starvation-induced autophagy, lysosomes are generated via de novo biogenesis under the control of TFEB (transcription factor EB), or by the recycling of autolysosome membranes via autophagic lysosome reformation (ALR). However, these lysosome repopulation processes do not operate under nutrient-rich conditions. In our recent study, we identify a sequential phosphoinositide conversion pathway that enables lysosome repopulation under nutrient-rich conditions to facilitate basal autophagy. Phosphatidylinositol-3,4-bisphosphate (PtdIns3,4P
2
) signals generated downstream of phosphoinositide 3-kinase alpha (PI3Kα) during growth factor stimulation are converted to phosphatidylinositol-3-phosphate (PtdIns3P) on endosomes by INPP4B (inositol polyphosphate-4-phosphatase type II B). We show that PtdIns3P is retained as endosomes mature into endolysosomes, and serves as a substrate for PIKFYVE (phosphoinositide kinase, FYVE-type zinc finger containing) to generate phosphatidylinositol-3,5-bisphosphate (PtdIns3,5P
2
) to promote SNX2-dependent lysosome reformation, basal autophagic flux and protein aggregate degradation. Therefore, endosome maturation couples nutrient signaling to lysosome repopulation during basal autophagy by delivering PI3Kα-derived PtdIns3P to endolysosomes for PtdIns(3,5)P
2
-dependent lysosome reformation.
Abbreviations: ALR: autophagic lysosome reformation; INPP4B: inositol polyphosphate-4-phosphatase type II B; PI3Kα: phosphoinositide 3-kinase alpha; PIKFYVE: phosphoinositide kinase FYVE-type zinc finger containing; PtdIns3P: phosphatidylinositol-3-phosphate; PtdIns(3,4)P
2
: phosphatidylinositol-3,4-bisphosphate; PtdIns(3,5)P
2
phosphatidylinositol-3,5-bisphosphate; SNX2 sorting nexin 2; PIK3C3/VPS34 phosphatidylinositol 3-kinase catalytic subunit type 3.
Autophagic lysosome reformation (ALR) recycles autolysosome membranes formed during autophagy, to make lysosomes and is essential for continued autophagy function. Localized membrane remodeling on ...autolysosomes leads to the extension of reformation tubules, which undergo scission to form new lysosomes. The phosphoinositides phosphatidylinositol-4-phosphate (PtdIns4P) and phosphatidylinositol-4,5-bisphosphate (PtdIns4,5P
2
) induce this remodeling by recruiting protein effectors to membranes. We identified the inositol polyphosphate 5-phosphatase INPP5K, which converts PtdIns(4,5)P
2
to PtdIns4P is essential for ALR in skeletal muscle. INPP5K mutations that reduce its 5-phosphatase activity are known to cause muscular dystrophy, via an undefined mechanism. We generated skeletal muscle-specific inpp5k knockout mice which exhibited severe muscle disease, with lysosome depletion and marked autophagy inhibition. This was due to decreased PtdIns4P and increased PtdIns(4,5)P
2
on autolysosomes, causing reduced scission of reformation tubules. ALR was restored in cells with loss of INPP5K by expression of wild-type INPP5K, but not muscle-disease causing mutants. Therefore on autolysosomes, both PtdIns(4,5)P
2
generation and its removal by INPP5K is required for completion of ALR. Furthermore, skeletal muscle shows a dependence on the membrane recycling ALR pathway to maintain lysosome homeostasis and ensure the protective role of autophagy against disease.
The regulation of autophagy-dependent lysosome homeostasis in vivo is unclear. We showed that the inositol polyphosphate 5-phosphatase INPP5K regulates autophagic lysosome reformation (ALR), a ...lysosome recycling pathway, in muscle. INPP5K hydrolyzes phosphatidylinositol-4,5-bisphosphate PI(4,5)P2 to phosphatidylinositol 4-phosphate PI(4)P, and INPP5K mutations cause muscular dystrophy by unknown mechanisms. We report that loss of INPP5K in muscle caused severe disease, autophagy inhibition, and lysosome depletion. Reduced PI(4,5)P2 turnover on autolysosomes in Inpp5k-/- muscle suppressed autophagy and lysosome repopulation via ALR inhibition. Defective ALR in Inpp5k-/- myoblasts was characterized by enlarged autolysosomes and the persistence of hyperextended reformation tubules, structures that participate in membrane recycling to form lysosomes. Reduced disengagement of the PI(4,5)P2 effector clathrin was observed on reformation tubules, which we propose interfered with ALR completion. Inhibition of PI(4,5)P2 synthesis or expression of WT INPP5K but not INPP5K disease mutants in INPP5K-depleted myoblasts restored lysosomal homeostasis. Therefore, bidirectional interconversion of PI(4)P/PI(4,5)P2 on autolysosomes was integral to lysosome replenishment and autophagy function in muscle. Activation of TFEB-dependent de novo lysosome biogenesis did not compensate for loss of ALR in Inpp5k-/- muscle, revealing a dependence on this lysosome recycling pathway. Therefore, in muscle, ALR is indispensable for lysosome homeostasis during autophagy and when defective is associated with muscular dystrophy.
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