Research in the last decade has clearly revealed a critical role of prostate cancer stem cells (PCSCs) in prostate cancer (PC). Prostate stem cells (PSCs) reside in both basal and luminal layers, and are the target cells of oncogenic transformation, suggesting a role of PCSCs in PC initiation. Mutations in PTEN, TP53, and RB1 commonly occur in PC, particularly in metastasis and castration-resistant PC. The loss of PTEN together with Ras activation induces partial epithelial–mesenchymal transition (EMT), which is a major mechanism that confers plasticity to cancer stem cells (CSCs) and PCSCs, which contributes to metastasis. While PTEN inactivation leads to PC, it is not sufficient for metastasis, the loss of PTEN concurrently with the inactivation of both TP53 and RB1 empower lineage plasticity in PC cells, which substantially promotes PC metastasis and the conversion to PC adenocarcinoma to neuroendocrine PC (NEPC), demonstrating the essential function of TP53 and RB1 in the suppression of PCSCs. TP53 and RB1 suppress lineage plasticity through the inhibition of SOX2 expression. In this review, we will discuss the current evidence supporting a major role of PCSCs in PC initiation and metastasis, as well as the underlying mechanisms regulating PCSCs. These discussions will be developed along with the cancer stem cell (CSC) knowledge in other cancer types.

Androgen deprivation therapy (ADT) has been the standard care for patients with advanced prostate cancer (PC) since the 1940s. Although ADT shows clear benefits for many patients, castration-resistant prostate cancer (CRPC) inevitably occurs. In fact, with the two recent FDA-approved second-generation anti-androgens abiraterone and enzalutamide, resistance develops rapidly in patients with CRPC, despite their initial effectiveness. The lack of effective therapeutic solutions towards CRPC largely reflects our limited understanding of the underlying mechanisms responsible for CRPC development. While persistent androgen receptor (AR) signaling under castration levels of serum testosterone (<50 ng/mL) contributes to resistance to ADT, it is also clear that CRPC evolves via complex mechanisms. Nevertheless, the physiological impact of individual mechanisms and whether these mechanisms function in a cohesive manner in promoting CRPC are elusive. In spite of these uncertainties, emerging evidence supports a critical role of prostate cancer stem-like cells (PCSLCs) in stimulating CRPC evolution and resistance to abiraterone and enzalutamide. In this review, we will discuss the recent evidence supporting the involvement of PCSLC in CRPC acquisition as well as the pathways and factors contributing to PCSLC expansion in response to ADT.

Alzheimer's disease (AD) is the most common type of neurodegenerative disease. Its typical pathology consists of extracellular amyloid-β (Aβ) plaques and intracellular tau neurofibrillary tangles. Mutations in the APP, PSEN1, and PSEN2 genes increase Aβ production and aggregation, and thus cause early onset or familial AD. Even with this strong genetic evidence, recent studies support AD to result from complex etiological alterations. Among them, aging is the strongest risk factor for the vast majority of AD cases: Sporadic late onset AD (LOAD). Accumulation of DNA damage is a well-established aging factor. In this regard, a large amount of evidence reveals DNA damage as a critical pathological cause of AD. Clinically, DNA damage is accumulated in brains of AD patients. Genetically, defects in DNA damage repair resulted from mutations in the BRAC1 and other DNA damage repair genes occur in AD brain and facilitate the pathogenesis. Abnormalities in DNA damage repair can be used as diagnostic biomarkers for AD. In this review, we discuss the association, the causative potential, and the biomarker values of DNA damage in AD pathogenesis.Int. J. Mol. Sci. 2020, 21, 1666 2 of 26 amyloid (senile) plaques in AD brain [9][10][11]. Furthermore, CDK5 activities affect DNA damage response [12], supporting a linkage of DNA damage with AD [13,14].Aβ peptides are directly produced by sequential cleavages of APP by βand γ-secretase; the proteolytic c-terminal fragment of APP (CTFβ) of β-secretase is cleaved within the cell membrane by γ-secretase to generate neurotoxic Aβ peptides with length ranging from 38-43 residues [15][16][17][18][19]. The 40 residue Aβ peptide (Aβ 1-40 ) is the major product, accounting for more than 50% of Aβ peptides [9,17]. Although the Aβ 1-42 peptide consists of less than 10% of Aβ peptides [16,17], it is more neurotoxic and associates with a higher risk of AD because of its propensity of aggregation [9]. The importance of Aβ in AD pathogenesis is illustrated by mutations of APP, PSEN1, and PREN2 genes in familial AD with the latter two encoding the presenilin 1 and presenilin 2 subunit of γ-secretase. Individuals with these mutations develop early onset dementia in an autosomal-dominant manner [20]; the typical onset starts between 30 and 50 years of age in PSEN1 mutant carriers with some being affected at in their 20s [20,21]. γ-secretase with mutant presenilin 1 or presenilin 2 subunit favors Aβ 1-42 production [16,17]. These genetic observations led to formation of the amyloid cascade hypothesis, in which abnormal Aβ drives AD pathogenesis via regulating other pathological events including tau pathology [22][23][24][25][26][27]. This hypothesis is supported by the similar pathological features between familial AD and sporadic late onset AD (LOAD) [20]. Although familial AD constitutes less than 1% of AD cases [28,29], the hypothesis has been widely accepted to guide research in advancing the understanding of both familial AD and LOAD in the past two decades [30,31].Nonetheless, it is becoming in...