PTPRF as a novel tumor suppressor through deactivation of ERK1/2 signaling in gastric adenocarcinoma

Figures & data

Table 1 Correlations between PTPRF expression and patient features

Factors	Cases	PTPRF level		P-value
	(n=115)	Low (n=58)	High (n=57)
Age				0.790
≤50 years	45	22	23
>50 years	70	36	34
Sex				0.395
Female	40	18	22
Male	75	40	35
Tumor size				0.070
≤5 cm	67	29	38
>5 cm	48	29	19
Differentiation				0.299
Good/moderate	63	29	34
Poor	52	29	23
Localization				0.096a
Upper gastric	22	15	7
Lower gastric	93	43	50
TNM stage				0.001*
I/II	47	15	32
III/IV	68	43	25

Notes:

a Fisher’s exact test, due to limited cases;

* P<0.05 (χ²).

Figure 1 PTPRF is downregulated in gastric adenocarcinoma tissue.

Notes: (A) Real-time PCR quantification of PTPRF mRNA levels in gastric adenocarcinoma tissue and matched adjacent nontumoral tissue (n=27). The mRNA expression of PTPRF in gastric adenocarcinoma tissue was significantly lower than in nontumoral tissue. (B) PTPRF showed a lower protein level in MKN45 tumor cells than normal GES1 epithelial cells. (C) Effect of PTPRF mRNA level on the overall survival of gastric adenocarcinoma patients (data generated from Cancer Genome Atlas database), showing its possible antitumor roles. Representative immunohistochemistry (IHC) results of PTPRF protein expression in adjacent nontumoral tissue (D) and gastric adenocarcinoma tissue (E), showing positive staining in both nucleus and cytoplasm. (F) Representative high expression of PTPRF in gastric adenocarcinoma tissue (IHC score 12). *P<0.05 (paired Student’s t-test); bar 100 µm.

Table 2 Kaplan–Meier OS analyses

Factors	OS, months (mean ± SD)	5-year OS (%)	P-value
Age			0.453
≤50 years	61.7±3.0	69.0
>50 years	59.2±2.3	59.7
Sex			0.889
Female	60.4±3.2	61.6
Male	60.0±2.3	64.7
Tumor size			0.065
≤5 cm	62.8±2.1	68.5
>5 cm	56.3±3.3	57.1
Differentiation			0.415
Good/moderate	61.9±2.4	66.3
Poor	57.8±2.8	61.0
Localization			0.088
Upper gastric	52.7±4.4	46.2
Lower gastric	61.4±2.0	66.9
TNM stage			0.001a
I/II	66.8±2.3	78.3
III/IV	54.6±2.4	53.6
PTPRF level			<0.001a
Low	52.2±2.8	52.1
High	66.4±1.8	75.6

Note:

a P<0.05 (log-rank test).

Abbreviation: OS, overall survival.

Figure 2 Analysis of overall survival in gastric adenocarcinoma patients.

Notes: The overall survival curve was assessed by the Kaplan–Meier method (A). The effect of each variable was also evaluate: PTPRF level (B), patient age (C), sex (D), tumor size (E), tumor differentiation (F), tumor location (G), and TNM stage (H). *P<0.05 (log-rank test).

Table 3 Multivariate analysis

Factors	HR	95% CI	P-value
Tumor size (>5 vs ≤5 cm)	1.525	0.830–2.801	0.174
Localization (lower vs upper)	0.477	0.222–1.024	0.058
TNM stage (III/IV vs I/II)	2.447	1.163–5.151	0.018a
PTPRF (high vs low)	0.492	0.252–0.959	0.037a

Note:

a P<0.05 (Cox regression test).

Figure 3 PTPRF suppresses gastric adenocarcinoma progression by downregulating ERK activation.

Notes: (A) Western blot results showed that overexpressing PTPRF downregulated ERK-phosphorylation level. The activity of ERK downstream effectors, such as Mnk1 and Myc, was also inhibited by PTPRF. Silencing PTPRF exhibited opposite effects. (B) The proliferation of gastric adenocarcinoma cells was not affected by PTPRF, as revealed by MTT experiments (P>0.05). (C) The migration process of gastric adenocarcinoma cells was tested by transwell assays, revealing a negative correlation between PTPRF level and cell-migration capacity. (D) Matrigel-coated transwell chambers were used to evaluate the invasion process of gastric adenocarcinoma cells, which demonstrated that PTPRF knockdown promoted cell invasion whereas PTPRF overexpression inhibited cell invasion. Similarly, the migration (E) and invasion (F) capacities of MKN45 cells were both inhibited by U0126, a specific ERK inhibitor. *P<0.05 (Student’s t-test).