Homeostatic and tumourigenic activity of SOX2+ pituitary stem cells is controlled by the LATS/YAP/TAZ cascade

Abstract

29 30 SOX2 positive pituitary stem cells (PSCs) are specified embryonically and persist throughout 31 life, giving rise to all pituitary endocrine lineages. We have previously shown the activation 32 of the MST/LATS/YAP/TAZ signalling cascade in the developing and postnatal mammalian 33 pituitary. Here, we investigate the function of this pathway during pituitary development and 34 in the regulation of the SOX2 cell compartment. Through loss-and gain-of-function genetic 35 approaches, we reveal that restricting YAP/TAZ activation during development is essential 36 for normal organ size and specification from SOX2+ PSCs. Postnatal deletion of LATS 37 kinases and subsequent upregulation of YAP/TAZ leads to uncontrolled clonal expansion of 38 the SOX2+ PSCs and disruption of their differentiation, causing the formation of non-39 secreting, aggressive pituitary tumours. In contrast, sustained expression of YAP alone results 40 in expansion of SOX2+ PSCs capable of differentiation and devoid of tumourigenic potential. 41 Our findings identify the LATS/YAP/TAZ signalling cascade as an essential component of 42 PSC regulation in normal pituitary physiology and tumourigenesis. 43 44 45 46 47 48 Key words: pituitary stem cell, SOX2, Hippo, YAP, pituitary tumour 49 50 51 52 53 54 55 56 life 1, 2 . The pituitary gland is composed of three parts, the anterior, intermediate and posterior 62 lobes (AL, IL and PL, respectively). The AL and IL contain hormone-secreting cells, which 63 are derived from an evagination of the oral ectoderm expressing SOX2, termed Rathke's 64 pouch (RP). SOX2+ cells, both in the embryonic and adult pituitary, can differentiate into 65 three endocrine cell lineages, which are marked by transcription factors PIT1 (POU1F1) 3 , 66 TPIT (TBX19) 4 and SF1 (NR5A1) 5 , and differentiate into hormone-secreting cells 67 (somatotrophs, lactotrophs, thyrotrophs, corticotrophs, melanotrophs and gonadotrophs, 68which express growth hormone, prolactin, thyrotropin, adrenocorticotropin, gonadotropin and 69 melanotropin, respectively). SOX2+ PSCs acquire PROP1 and SOX9 expression 70 embryonically 2, 6 and are become highly proliferative during the first 2-3 weeks of life, in 71 concordance with major organ growth, after which they reach a steady low proliferative 72 capacity that contributes to maintain normal homeostasis and physiological adaptation of the 73 pituitary gland 7, 8 . 74 75Contrary to other organs, where somatic stem cells are shown to be able to become 76 transformed into cancer stem cells, the roles of SOX2+ PSCs in tumourigenesis remain poorly 77 understood, possibly due to the patchy knowledge of the pathways regulating SOX2+ PSC 78 fate and proliferation. Pituitary tumours are common in the population, representing 10-15% 79 of all intracranial neoplasms 9, 10 . Adenomas are the most common adult pituitary tumours, 80 classified into functioning, when they secrete one or more of the pituitary hormones, or non-81 functioning if they do not secrete hormones. In children, adamantinomatous 82 cranio...

Pituitary stem cells produce paracrine WNT signals to control the expansion of their descendant progenitor cells

“…Analysis of global gene expression signatures using 'Gene Set Enrichment Analysis' (GSEA)(Subramanian et al, 2005) identified a significant enrichment of molecular signatures related to EMT, adherens and tight junctions in the EGFP + fraction, characteristic of the SOX2 + population(Figure 3figure supplement 1B). The SOX2 + fraction also displayed enrichment for genes associated with several signalling pathways known to be active in these cells, including EGFR (Iwai-Liao et al, 2000), Hippo(Lodge et al, 2016;Lodge et al, 2019;Xekouki et al, 2019), MAPK(Haston et al, 2017), FGF(Higuchi et al, 2017), Ephrin(Yoshida et al, 2015;Yoshida et al, 2017) and p53 (Gonzalez-Meljem et al, 2017) (Figure 3figure supplement 1C, Supplementary File 1). Additionally, PI3K, TGF and BMP pathway genes were significantly enriched in the SOX2 + population(Figure 3figure supplement 1C, Supplementary File 1).…”

Requirement of FAT and DCHS protocadherins during hypothalamic-pituitary development

“…FAT4/DCHS1 may be involved in cell movements during development, which is consistent with their known role in planar cell polarity (10,11,25), often an important pathway during dynamic rearrangement and migration of cells. In the anterior pituitary they are unlikely to act upstream of YAP for this purpose, as previous work deregulating YAP levels during development did not result in medio-lateral morphogenesis defects (36).…”

“…The VECTOR Laboratories ImmPRESS kit was used for antibodies against SF1 according to the manufacturer's instructions. The PerkinElmer TSA kit was used for antibodies against DCHS2 and FAT2, as previously described (36). After primary antibody incubation, slides were washed in PBST, then incubated with appropriate secondary antibodies (biotinylated goat anti-rabbit, 1:300, Abcam ab6720; biotinylated goat anti-mouse, 1:300 Abcam ab6788) and incubated with fluorophore-conjugated streptavidin (1:500, Life Technologies, Thermo Fisher Scientific, S11223) for 1 hour at room temperature.…”

Single nucleus pituitary transcriptomic and epigenetic landscape reveals human stem cell heterogeneity with diverse regulatory mechanisms

“…The remaining large group of 6 clusters expressed SOX2 , SOX9 , and the Hippo pathway effectors WWTR1 (a.k.a. TAZ ) and YAP1 ( 17 and reviewed in 18 ; Fig. 3d and Supplementary Fig.…”