Literature search
Our search strategy preliminarily determined 329 potential records. There were 173 items remained after removing the duplicates. Of these, 48 studies were removed through perusing titles and abstracts. And then, reviews, editorials, letters, conference abstracts, retracted articles, not full texts in English, and studies on cancer cells or animal models were excluded. Subsequently, 18 studies lacking insufficient data were rejected. Finally, 19 studies containing 3775 GC patients were included for this analysis. The selection process was shown in Fig. 1.
Study Characteristics
All included studies were from China, Japan and Korea, and published between 2012 and 2019. These studies involve the following HOX proteins: HOXB9 (15), HOXD10 (16), HOXA5 (17, 18), HOXA10(19–21), HOXA13 (22, 23), HOXC6 (24), HOXB7(25, 26), HOXA1 (27), HOXA9 (28), HOXC9 (29), HOXC10(30), HOXD4 (31), HOXA11 (32) and HOXD9 (33). These studies explored the prognostic value of HOX proteins expression for OS or disease-free survival (DFS), and the correlation between HOX proteins expression and clinicopathological parameters in GC. The HOX genes expression on protein level was detected by immunohistochemical staining. All included studies divided HOX proteins expression into high(positive) and low(negative) groups, but the cut-off value was slightly distinct among these studies. The detailed studies characteristics were listed in Table 1.
Table 1
Characteristics of the included studies
First author | Year | Country | HOX protein | Expression | Sample size (high/low) | Cut-off value | Survival | Survival analysis | HR availability | NOS score |
Sha et al (15) | 2013 | China | HOXB9 | Down-regulated | 190(86/104) | IS:4 | OS | U, M | Text | 7 |
Wang et al (16) | 2015 | China | HOXD10 | Down-regulated | 436(242/194) | IS:4 | OS | U | Kaplan-Meier curves | 7 |
Peng et al (17) | 2018 | China | HOXA5 | Down-regulated | 81(29/52) | IS:4 | OS | U, M | Text | 8 |
Wu et al (18) | 2019 | China | HOXA5 | Down-regulated | 124(60/64) | median value | OS, DFS | U | Kaplan-Meier curves | 7 |
Sentani et al (19) | 2012 | Japan | HOXA10 | Up-regulated | 749(221/528) | percentage of stained cancer cells = 10% | OS | U, M | Text | 7 |
Han et al (22) | 2013 | China | HOXA13 | Up-regulated | 132(103/29) | IS:3 | OS, DFS | U, M | Text | 7 |
Lim et al (20) | 2013 | Korea | HOXA10 | Up-regulated | 57(29/28) | compare to the staining smooth muscle | OS | U | Kaplan-Meier curves | 7 |
Zhang et al (24) | 2013 | China | HOXC6 | Up-regulated | 161(76/85) | IS:2 | OS | U | Kaplan-Meier curves | 8 |
Han et al (21) | 2015 | China | HOXA10 | Up-regulated | 264(159/105) | IS:2 | OS, DFS | U, M | Text | 6 |
Tu et al (25) | 2015 | China | HOXB7 | Up-regulated | 96(66/30) | IS:2 | OS, DFS | U, M | Text | 8 |
Yuan et al (27) | 2016 | China | HOXA1 | Up-regulated | 264(144/120) | IS:3 | OS, DFS | U | Text | 6 |
He et al (26) | 2017 | China | HOXB7 | Upregulated | 330(195/135) | IS:4 | OS | U | Kaplan-Meier curves | 8 |
Ma et al (28) | 2017 | China | HOXA9 | Up-regulated | 128(88/40) | IS:4 | OS | U, M | Text | 8 |
Han et al (23) | 2018 | China | HOXA13 | Up-regulated | 264(186/78) | IS:3 | OS, DFS | U, M | Text | 6 |
Peng et al (29) | 2018 | China | HOXC9 | Up-regulated | 95(68/27) | IS:4 | OS | U, M | Text | 7 |
Yao et al (30) | 2018 | China | HOXC10 | Up-regulated | 73(38/35) | IS:4 | OS | U, M | Text | 7 |
Liu et al (31) | 2019 | China | HOXD4 | Up-regulated | 127(68/59) | IS:7 | OS | U, M | Text | 7 |
Wang et al (32) | 2019 | China | HOXA11 | Up-regulated | 114(58/56) | IOD/Area = 0.31 | OS | U, M | Text | 6 |
Zhu et al (33) | 2019 | China | HOXD9 | Up-regulated | 90(55/35) | IS:3 | OS | U | Kaplan-Meier curves | 6 |
OS: overall survival; DFS: disease free survival; U: univariate analysis; M: multivariate analysis; IS: immunostaining score; IOD: integrated option density; NOS: Newcastle-Ottawa Scale. |
Correlation Of Hox Proteins Expression With Prognosis
All of the 19 included studies contained a total of 14 HOX proteins, and decreased expression of HOXB9, HOXD10 and HOXA5 inhibited GC progression. In contrast, HOXA13, HOXC6, HOXB7, HOXA1, HOXC9, HOXC10, HOXD4, HOXA11 and HOXD9 were highly expressed and acted as tumor promotors in GC. Besides, it must be mentioned that HOXA10 expression was increased in GC, but its role in the prognosis of GC was controversial. In a pooled analysis including all studies with data on prognostic effect for HOX proteins in GC, the huge heterogeneity among pooled HR of OS was observed. The subgroup analysis by expression level was performed and the results revealed different trends between down-regulated subgroup and up-regulated subgroup. High expression of HOX proteins in the down-regulated subgroup was associated with a good prognosis of GC (pooled HR: 0.46, 95% CI: 0.36–0.59, I2 = 3.1%, p = 0.377), while over-expressed HOX proteins in the up-regulated subgroup related to poor OS (pooled HR: 2.59, 95% CI: 1.79–3.74, I2 = 73.5%, p = 0.000) (Fig. 2A). The cause for the high heterogeneity of up-regulated subgroup might be that HOXA10 had distinct prognostic values in the existing studies. The result of up-regulated subgroup analysis excluding HOXA10 suggested over-expressed HOX proteins significantly indicated poor prognosis. (pooled HR = 3.03, 95% CI: 2.45–3.74, I2 = 16.5%, p = 0.283) (Fig. 3). DFS was available from 6 studies including 5 HOX proteins. HOXA5 was favorable to DFS of GC (pooled HR = 0.46, 95% CI: 0.23–0.91). Contrarily, HOXA13, HOXA10, HOXB7 and HOXA1 acted as unfavorable factors for DFS in GC (pooled HR = 3.77, 95% CI: 2.61–5.45) (Fig. 2B).
Correlation Of Hox Proteins Expression With Clinicopathological Parameters
A total of 17 studies with 2899 patients were included to detect the relationship between HOX proteins expression and tumor stages of GC. As shown in Fig. 4, the elevated expression of HOXB9 and HOXD10 were significantly correlated with the early TNM stage (HOXB9: OR = 0.22, 95% CI: 0.12–0.41, HOXD10: OR = 0.21, 95% CI:0.14–0.31), while the increased expression of HOXA13, HOXB7, HOXA1, HOXA9, HOXC9, HOXC10, HOXA11 and HOXD9 was notably associated with the advanced TNM stage. The pooled analysis of the relationship between HOX proteins expression and depth of tumor invasion showed that HOXD10 indicated low T category (HOXD10: OR = 0.20, 95% CI: 0.09–0.41), while HOXA13, HOXC6, HOXB7 and HOXA1 were observably related to high T category (HOXA13(2013): OR = 4.18, 95% CI: 1.75–10.01; HOXA13(2018): OR = 1.90, 95% CI: 1.08–3.35; HOXC6: OR = 3.55, 95% CI: 1.11–11.31; HOXB7(2015): OR = 3.44, 95% CI: 1.32–8.95; HOXB7(2017): OR = 10.14, 95% CI: 4.36–23.58; HOXA1: OR = 2.03, 95% CI: 1.18–3.48) (Fig. 5A). We pooled 11 studies including 2087 patients and found that HOXD10, HOXA5 and HOXC10 were associated with small tumor size (HOXD10: OR = 0.37, 95% CI: 0.25–0.54; HOXA5(2018): OR = 0.20, 95% CI: 0.07–0.55; HOXA5(2019): OR = 0.23, 95% CI: 0.08–0.67; HOXC10: OR = 0.38, 95% CI: 0.15–0.98), while the overexpression of HOXA10, HOXB7 and HOXD4 made tumor large (HOXA10(2015): OR = 2.39, 95% CI: 1.40–4.09; HOXB7(2017): OR = 2.60, 95% CI: 1.61–4.20; HOXD4: OR = 2.71, 95% CI: 1.28–5.74) (Fig. 5B). 16 studies with 3509 patients reported that HOXB9 and HOXD10 are unfavorable factors for lymph node metastasis in GC (HOXB9: OR = 0.35, 95% CI: 0.19–0.63; HOXD10: OR = 0.24, 95% CI: 0.16–0.37), the overexpression of HOXA13, HOXA1, HOXA9, HOXC10, HOXD4 and HOXD9 were correlated with the presence of lymph node metastasis (HOXA13(2013): OR = 2.38, 95% CI: 1.02–5.54; HOXA13(2018): OR = 2.38, 95% CI: 1.39–4.09; HOXA1: OR = 2.45, 95% CI: 1.49–4.04; HOXA9: OR = 2.68, 95% CI: 1.23–5.83; HOXC10: OR = 6.18, 95% CI: 2.22–17.18; HOXD4: OR = 5.53, 95% CI: 2.55–12.02; HOXD9: OR = 23.11, 95% CI: 6.04–88.49) (Fig. 6A). The pooled results revealed HOXD10 was not conducive to distant metastasis of GC (HOXD10: OR = 0.34, 95% CI: 0.19–0.60), but HOXC10 and HOXA11 promoted GC distant metastasis (HOXC10: OR = 5.55, 95% CI: 1.42–21.61; HOXA11: OR = 19.02, 95% CI: 1.07-337.91) (Fig. 6B). Besides, the up-regulation of HOXB7 was beneficial to vascular invasion in GC (HOXB7(2017): OR = 5.12, 95% CI: 3.18–8.23). (Fig. 6C). Moreover, HOXB9, HOXD10, HOXA5 and HOXC9 were favorable factors for well or moderate histological differentiation (HOXB9: OR = 0.17, 95% CI: 0.09–0.33, HOXD10: OR = 0.66, 95% CI: 0.44–0.99, HOXA5(2018): OR = 0.26, 95% CI: 0.10–0.68; HOXC9: OR = 0.28, 95% CI: 0.11–0.71), and overexpression of HOXA13, HOXA1, HOXA9 and HOXD9 related to the poorly differentiated status of GC (HOXA13(2013): OR = 2.41, 95% CI: 1.02–5.67; HOXA13(2018): OR = 1.84, 95% CI: 1.06–3.18; HOXA1: OR = 2.37, 95% CI: 1.41-4.00; HOXA9: OR = 4.98, 95% CI: 2.12 11.70; HOXD9: OR = 14.63, 95% CI: 4.81–44.43) (Fig. 7A). Additionally, HOXD10 and HOXB7 correlated with intestinal phenotype of GC (HOXD10: OR = 5.02, 95% CI: 3.34–7.57; HOXB7(2017): OR = 6.27, 95% CI: 3.81–10.31) (Fig. 7B). All enrolled HOX proteins in the pooled analysis had no significant association with the age (Fig. 8A), gender (Fig. 8B) or tumor location (Fig. 8C).
Sensitivity Analysis
Sensitivity analysis was performed to verify the robustness of our results. As shown in Fig. 9, the pooled HR was not significantly altered when removing any study, which confirmed the reliability of overall results for OS of GC.
Publication Bias
Begg’s test and Egger’s test were used to evaluate the publication bias. The result indicated there was no substantial publication bias (Fig. 10: Begg's test: p = 0.576, Egger’s test: p = 0.166).
Mechanisms Of Homeobox Proteins Acting On Gastric Cancer
As shown in Table 2, we generalized the molecular mechanisms how HOX proteins included in this study modulated carcinogenesis and development of GC (15–57). HOXB9, HOXD10 and HOXB7 were all implicated in the AKT pathway in GC. Notably, it is generally accepted that HOXA10 expression is up-regulated in GC, but its prognostic value in GC was contradictory. Ultimately, HOXA11 expression level and its effect in GC remain controversial for the moment.
Table 2
Action mechanisms of HOX proteins in gastric cancer
HOX proteins | Expression | Upstream | Downstream | Pathways | Reference |
HOXB9 | Down-regulated | NA | NA | ↓cells proliferation, migration and invasion; ↑MET; AKT and NF-κB pathway | (15,34,35) |
HOXD10 | Down-regulated | miR-10b, miR-92b-3p | IGFBP3 | ↓cells proliferation, migration and invasion; AKT pathway; | (16,36–39) |
HOXA5 | Down-regulated | miR-196a | NA | ↓cells G1-S transition, proliferation and colony formation; ↓angiogenesis | (17,18) |
HOXA10 | Up-regulated | NA | miR-196b-5p, BCL2 | ↑cells viability, proliferation, colony information, migration and invasion; ↓apoptosis; ↑tumor metastasis; JAK1/STAT3 signaling; HOXA10/miR-196b-5p axis; ↓cells growth, motility and invasive activity; | (19–21,46–48) |
HOXA13 | Up-regulated | lncRNA HOTTIP | DHRS2, cadherin17 | ↑cells proliferation, migration and invasion; ↑EMT; TGF-β pathway, ERK1/2 pathway, Wnt/β-catenin pathway, MDM2-p53 pathway; chemotherapy resistance to 5-FU | (22,23,40–43) |
HOXC6 | Up-regulated | lncRNA HOTAIR | NA | ↑cells proliferation, colony formation, migration and invasion; ERK signaling; | (24,44,45) |
HOXB7 | Up-regulated | NA | NA | ↑cells G1-S transition, proliferation, migration and invasion; ↑EMT; ↓apoptosis; AKT/MAPK pathway; Src-FAK pathway; PIK3R3/ AKT pathway; | (25,26,49,50) |
HOXA1 | Up-regulated | NA | NA | ↑cells proliferation, invasion and migration; ↑cyclin D1 | (27) |
HOXA9 | Up-regulated | miR-182 | NA | ↑cells proliferation, migration and invasion; ↑tumor progression; | (28,51) |
HOXC9 | Up-regulated | miR-26a | NA | ↑EMT and stem cell-like phenotypic acquisition; ↑tumor metastasis; | (29) |
HOXC10 | Up-regulated | miR-136 | CST1 | ↑cells migration and invasion; ↑tumor growth and peritoneal metastasis; ATM/NF-kB pathway; MAPK signaling | (30,52–55) |
HOXD4 | Up-regulated | NA | NA | ↑cells proliferation, migration and invasion; ↑c-Myc and cyclinD1 | (31) |
HOXA11 | Controversial | STAT3 | STAT3 | Wnt pathway | (32,56,57) |
HOXD9 | Up-regulated | NA | RUFY3 | ↑cells proliferation, invasion and migration; ↑tumorigenesis and metastasis | (33) |
↓: inhibit; ↑: promote; NA: not available; MET: mesenchymal epithelial transition; IGFBP3: insulin-like growth factor binding protein-3; BCL2: B cell lymphoma-2; DHRS2: dehydrogenase/reductase 2; EMT: epithelial mesenchymal transition; MDM2: murine double minute 2; 5-FU: 5-fluorouracil; PIK3R3: phosphoinositide-3-kinase, regulatory subunit 3; CST1: cystatin 1; RUFY3: RUN and FYVE domain containing 3. |