Original ArticlesPancreatic DCLK1+ cells originate distinctly from PDX1+ progenitors and contribute to the initiation of intraductal papillary mucinous neoplasm in mice
Introduction
Doublecortin CaM kinase-like-1 (DCLK1, previously referred to as DCAMKL-1) is originally identified in the developing nervous system [1,2]. Its expression is one of the molecular features of gastrointestinal tuft cells [3,4]. DCLK1 regulates the polymerization of microtubules in many mammalian cells by its N-terminal microtubule binding domain [5]. Its C-terminal kinase domain can be cleaved and released from the microtubule anchorage domain by cysteine protease calpain [6]. In addition, DCLK1 has recently been demonstrated as a putative biomarker of tumor-initiating cells in genetically engineered mouse model (GEMMs) for various types of tumors, including pancreatic cancer [[7], [8], [9], [10], [11], [12]]. For example, DCLK1-expressing cells in intestinal tumors have been thought to be tumor progenitor cells, as diphtheria toxin-mediated ablation of DCLK1+ cells led to tumor regression [7,10]. However, in human gastrointestinal tumors, DCLK1-expressing cells were mainly observed at the early stages of tumorigenesis such as metaplastic and hyperplastic lesions [4,13]. Increasing evidence also exhibit that DCLK1 might be a differentiated marker of mature tuft cells in the intestine, rather than a stem or progenitor cell marker in normal and tumor tissues [14,15].
Pancreatic intraductal papillary mucinous neoplasms (IPMN) is one of the three known precursors of invasive pancreatic ductal adenocarcinoma (PDA). High frequency of DCLK1+ cells has been also reported in precursor lesions of pancreatic cancer such as pancreatic intraepithelial neoplasias (PanINs) in both human and mouse [8,[15], [16], [17]]. These morphologically tuft-like DCLK1-expressing cells have been recognized as putative stem/progenitor cells in pancreatic tissues of these GEMMs with PanIN/PDA histologic presentation [18], but how DCLK1+ cells are involved in the genesis of pancreatic IPMNs has not been explored.
TGF-β superfamily signaling plays a pivotal role in determining the pathogenesis of PDA derived from PanINs or IPMNs [[19], [20], [21], [22]]. We have reported that mutant Kras in the context of inactivated activin signaling promotes the development of IPMN/PDA in our recently established Acvr1bflox/flox;LSL-KrasG12D;Pdx1-Cre GEMM [22,23]. In contrast, mPanIN/PDA pathogenesis is the major histologic presentation in the LSL-KrasG12D; Pdx1-Cre GEMM with or without additional p16 inactivation [24,25]. Using these established GEMMs with specific IPMN or PanIN genesis, we observed that DCLK1+ cells were predominately detected in the pancreatic tissues with activated mutant Kras and not in the Cre-negative normal control mice. Pancreatic DCLK1+ cells shared the molecular features of intestinal tuft cells but not the IPMN tumor cells. Lineage tracing demonstrated that these pancreatic DCLK1-expressing cells originated from cell lineage distinct from PDX1+ progenitors. Furthermore, DCLK1+ cells could be detected in the early stage of tumorigenesis, such as in the proliferative acinar clusters prior to the formation of metaplastic ductal cells, and were further enriched at the base of IPMN tumors.
Section snippets
Mouse strains
All animal experiments described here were approved by Columbia University Animal Care and Use Committees. LSL-KrasG12D; Pdx1-Cre (thereafter called KP) mice [24] with full spectrum of PanINs and low progression to invasive PDA were used as the representative PanIN model in this study. Acvr1bflox/flox; LSL-KrasG12D; Pdx1-Cre (thereafter called AKP) mice [22] (backcrossed to C57BL/6 background), a recently characterized GEMM for IPMN, were bred into R26REYFP mice (
DCLK1+ cells significantly accumulated in the precursor lesions of pancreatic tumors
We have previously reported a GEMM for IPMNs (Acvr1bflox/flox;LSL-KrasG12D;Pdx1-Cre or the AKP GEMM) [22] which was generated by tissue-specific and conditional inactivation of the Acvr1b gene (Acvr1bflox/flox) [23] in the pancreas in the context of oncogenic Kras activation (LSL-KrasG12D;Pdx1-Cre or the KP GEMM) [24]. To explore the potential role of DCLK1-expressing cells in the genesis of IPMNs, DCLK1-expressing cells were investigated in the pancreatic tissues of the AKP GEMM by
Discussion
DCLK1+ cells have been previously demonstrated being involved in both intestinal regeneration homeostasis and response to pancreatic inflammatory injury [7,17]. The inflammation-induced regeneration seems to be essential for oncogene-related carcinogenesis [41]. The mechanisms for the interaction between oncogene-induced inflammation and tumorigenesis in pancreas are not clear. In this study, we showed that DCLK1+ cells are mainly enriched in inflammatory lesions ADM and precancerous lesions
Conflicts of interest statement
There is no conflict of interest pertaining to this publication to be disclosed by any of the authors.
Acknowledgements
We want to acknowledge Dr. Jessica Kandel for her generosity of sharing the Rag2−/−;Il2rg−/−;eGFP+/+ immunodeficient mice with us prior to its publication. This study was only possible with the support of the NIH/NCI R01 CA217207, NIH/NCI R01 CA178445.
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